I mean, I'm fully on board with not getting hung up on what's "correct", but these are words that do have a specific meaning and I do find it interesting that the preferred choice of words shifts (even if it is only caused by relatively few people, that actually think about their word choice there).

Specifically, "no problem" is kind of like saying "there's nothing to thank me for". And ultimately, it kind of says "I don't expect something in return".

Whereas "you're welcome" acknowledges that yes, I did help you, you are right to thank me for that, and also kind of "I would appreciate you returning the favor".

My personal theory is that the change in language happens, because we have a lot more contacts with strangers, either in big/foreign cities or online.
When you help a stranger, you know upfront that they won't be able to return the favor, simply because you won't stay in contact. So, not only should it definitely not be a personal sacrifice for you to help them, it also feels right to communicate that they don't owe you anything, so that they can go on in their life.