Why not? because it doesn't seem (to me) to make any sense.

You acted. you received some form of acknowledgement or appreciation for that action.

How is telling someone they are "welcome" meaningful? And while "no problem" might unfairly minimize the importance of the action, or serve to deflect praise from yourself, at least it is meaningful - it did not cause me any problems to do this action. The Spanish de nada is similar, and even more dismissive - essentially saying it was nothing.

Yes, languages and specifically idioms tend to defy understanding and logic, I can't see an appeal to understanding over one response choice being met with an appeal to defy understanding for another.