Do you think it’s rude to not say “you’re welcome” when being thanked?

I think it’s rude and it pisses me off. When I thanked some of the coworkers, they don’t respond at all but they responded to the kids. Are adults not that important?

My dad or siblings don’t say you’re welcome at all. Some say “no problem” which is cool.

What’s wrong saying “You’re Welcome”? Be honest why don’t you say it?