have u ever thought about the phrase 'you're welcome'

I think it means more that you are expressing that you are always welcome to do that particular thing. It's the difference between, "You are welcome to ask again" and "It was no problem that you asked but maybe it might be next time."
For example, if Jamie asked me to proof read an essay and I did, and she thanked me, I would say "you're welcome" or "any time" because she's always welcome to ask me because I have no problem doing it.
But if say an old high school class mate that I wasn't terribly close to asked the same thing, and thanked me when I did, I'd say, "No problem" because this time it wasn't really a problem, but I'm not close enough to them to want to do it again.

Welcome can mean both embrace and encourage, and a lot of words in the english language will show a variety of different connotations.