Yes,
it is beautiful movie, fun, interesting, good quality Xmas movie.

Well here we are some…40 years later, still talking about it
So it clearly left an impression and has worked its way into your mind enough to still wish to discuss it. That's the magic of cinema

True. I watched it in cinema in 1985-ish.
I lived in a former communist country where Christmas was not allowed, so Christmas music was beautiful to listen on the screen.
My reasoning about Gremlins is rooted in childish mentality and mixed with popcorn fun emotions.

Well you have to realise the situation for any of that to make sense.
It is just a story for children though, so sometimes taking it at face value is worth it more

Yep.
I made logical fallacy.
I have seen Gremlins from Hollywood point of view - being interesting character and not actual biological entity with its own physical laws and impulses.

If you think of the mogwai/gremlins as a species, this is how they would go about their business

-interesting take.

I don't think you are Ranc
Gizmo is the Trojan horse of his species. He gets into a cultivated and successful species with his cutesy looks and agreeable nature. He truly believes he is as good as we all think he is, the perfect sleeper agent.
Then, once settled in, his biology kicks in and he gets up to low level mischief which is perfectly understandably for a toddler or puppy. However this latest misbehaving is actually his underlying procreative genetics kicking in with the idea of spreading its seed far and wide.
Be it having food left out, or being squirted with water, his social cues always make something occur which will proliferate his continuance in some shape or form. The ultimate predator.
Think of Gizmo like a cute facehugger from the movie Alien. Once he's in, it is in his genes to make sure he gets everywhere and takes control. He doesn't even know it.
And so Gizmo didn't stay put because that's his natural drive to somehow procreate

That makes sense,
sometimes I intellectualize too much of everything.

He is still just an animal. I'm guessing he doesn't like being cooped up.
So many stories, so little time.