Right. Bob didn't seem like a threat to the family. He had issues, but so does everyone. He could even relate to some of the stuff the family talked to him about.

The family was on vacation and Bob equaled fun. Leo even on vacation never equaled fun. His daughter's comment to her father about him never being a child was very revealing. She also described Bob as "he's fun" which Leo didn't get that about Bob nor why she didn't think her father was.
Leo was a pretentious control freak and anyone living with that for years could easily be drawn to Bob while on vacation.

I just watched this again on Netflix, and agree that Leo was a stuffy uptight douche bag, but then again, Bob is so annoying that, in reality, nobody with a bit of sanity would want him around. The wife ignoring the fact that a psychaitric patient has just shown up on their vacation and is so la dee da about it is incomprehensible.
A L C _ H _ L - Sometimes alcohol
is
the answer

Because the only man in their lives was a self-absorbed, snotty douche-bag. Bob was (as the daughter put it) fun and sensitive.
Anyone here mentions Hotel California dies before the first line clears his lips.

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Bob. Stupid autocorrect.

But was able to talk in a natural and relaxed manner.

I did and I was just asking out of curiousity, I agree Bob was a huge breath of fresh air compared to Leo

Didn't you watch the movie ? None of the them were enjoying themselves before Bob showed up. Their father was basically trying to control every single aspect of the vacation with endless rules. Bob showed up and was a breath of fresh air. They were ready to grab on to anything which could provide some kind of fun.

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Well, Bob seemed like a nice person to them and fun to be around with. Maybe Leo wasn't like that.

Leo = uptight, strict, obsessed with his profession
Bob = goofy, fun, childlike

In addition to what everyone else said, I think the family was happy to see someone new and hang out with him. He was different, he listened and he didn't push them.
Michael.JACKSON

I watched this movie last night and was wondering the same thing myself lol
Personally, If it had been me, Bob would have driven me crazy. His constant verbalizations would have done it lol.I can completely understand Richard Dryfusses character going nuts.

Because Bob is a sincerely nice person who seems to genuinely care about what they want and doesnt seem to want them to revolve around him. He doesnt seem judgemental and seems very innocent and in need of "family"