I think the premise was not that Daphne pretended not to notice that Niles had a crush on her but that Daphne didn't realize he had a crush on her, which I agree was ridiculous. To answer your question though I think a lot of times a woman will pretend not to notice a man has crush on her because if she doesn't feel the same she thinks it's kinder to pretend not to know than to hurt him. She hopes if she doesn't acknowledge it eventually he'll move on and that will be that.
Also to be honest most women want the man to make the first move. Women love confident men and tend to think they will be better lovers. I don't know that that is always true but it is the initial perception.

For Daphne specifically, I read that the actress herself interpreted her obliviousness as her character thinking Niles was too good for her so she never took his affections too seriously.

Also Daphne was a dingbat.
Religion is regarded by the common people as true, by the wise as false, and by rulers as useful.

I'm male and I've known two girls who liked me when I was completely oblivious. They were good friends of mine and it never occurred to me that they had romantic feelings. It's quite plausible that Daphne would be equally in the dark, though the whole thing was exaggerated for comedy.
Sometimes one can be oblivious, even though there are signals and other times one can see signals which aren't there. In real life it is not always or at least not readily clear, what people see in their relationships with others. Even spouses don't always realize when their partner is cheating on them. (I don't want to know how deeply shocked some must be, when they're left and understand how many years they've believed a lie.)
But this is a sitcom and relationships are more clearly adn rather sharply defined for the viewer. Also, we often know more about the relationships than the characters themselves, because we see everything that is going on.

I can't comment on your general observations, but Daphne's obliviousness to Niles was part of the charm. Yes, he made it astonishingly obvious and that was the joke.
"That's nonsense. Dr Crane's always popping round with little gifts for me and he's not after anything."
Perspectives On Christmas is a good episode for showing how Daphne has a very different perception of what Niles says.
I'm male and I've known two girls who liked me when I was completely oblivious. They were good friends of mine and it never occurred to me that they had romantic feelings. It's quite plausible that Daphne would be equally in the dark, though the whole thing was exaggerated for comedy.

I understand what you are saying, but through conversations with my sister (who is Asexual) she tries not to notice when men look at her lustfully in public, the thing is it has got to the point where she no longer wants to pretend that something isn't happening, she'll look at them back as if to say "what the hell are you looking at?!" it's a realistic thing to do, isn't it better to acknowledge what is going on? it doesn't necessarily mean that a woman has to like being looked at lustfully.
Different cultures have different norms. I'm often shocked, being an American, when I watch English or French movies, and women speak right up to men who are ogling them as your sister does. It seems pretty cheeky but I kind of envy those women.
Of course a woman isn't obliged to acknowledge a man's crush on her, but wouldn't women feel they are in denial pretending that there isn't a problem and that everything's fine?!
It's easier to live in denial sometimes. For example, if the guy is a friend and you want to keep the friendship going, but have no interest in romance with him (this happened to me a couple times in my life).
Also, you're characterizing this as a "problem." As far as I can see, it's only a "problem" for the man in this situation. Why does the girl have any responsibility for the man's feelings?

I understand what you are saying, but through conversations with my sister (who is Asexual) she tries not to notice when men look at her lustfully in public, the thing is it has got to the point where she no longer wants to pretend that something isn't happening, she'll look at them back as if to say "what the hell are you looking at?!" it's a realistic thing to do, isn't it better to acknowledge what is going on? it doesn't necessarily mean that a woman has to like being looked at lustfully.
Of course a woman isn't obliged to acknowledge a man's crush on her, but wouldn't women feel they are in denial pretending that there isn't a problem and that everything's fine?!

a man blatantly looks at you like a piece of meat and you're not gonna notice that?
Maybe some women don't want to notice someone looking at them like a piece of meat?
I'm just stating what nobody else notices or wants to acknowledge.
I think that most people acknowledge that a woman isn't obliged to acknowledge a man's crush on her.

You have worded that in a very offensive way, I say that as I can never realise other peoples emotions so have been called dumb, yet in fact I have a Mensa level IQ and amazing puzzle solving abilities.
So before you state ignorance like someone isn't very intelligent, think you yourself are not very intelligent to have a ignorant view!

I had the impression that Daphne knows very well what is going on around her, except for Niles' crush on her. On the other hand, she is rather attractive and she probably gets looked at often, so she doesn't mind when Niles looks at her like she's a piece of meat. Maybe being fancied means not much to her. It is much later on - I believe the sixth season - when she learns of Niles' real feelings for her and then she suddenly realizes that she has more serious feelings for him too. I believe love can go these twisted ways. I think compared to what strange ways love can go in real life, the love of Daphne and Niles seems rather normal.

professor_of_gamez: You are probably right, Daphne must have been "slow", i'm not being horrible but in real life as well there are a lot of dumb people who don't notice things that are right in their faces. I don't like to think there are people that dumb in the world, but there actually is. Now when it comes to Daphne it is never made clear whether the writers wanted her to be not very intelligent or just consumed with herself that she doesn't notice her surroundings.

Daphne always struck me as a little "slow." I mean come on Niles sniffed her hair on multiple occasions (she even noticed once), tried on jewelry and dresses. The latter should have been a tip off (since it had been said that she had met Maris, and Maris was said to be a foot shorter).

It's a test of courage. If he's too callow to even express himself well, then he can't be a good lover, can he?

Most women I know say the man has to make the first move.
Religion is regarded by the common people as true, by the wise as false, and by rulers as useful.

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Maybe they're just playing hard to get.