This, but I think a lot of people are over analyzing the question and not answer the actual premise of “why doesn’t it fall in?” I assume this is based on the idea that nucleus should be + and electron - so why don’t they just lump together?

The answer is the strong force which prevents them from coming into contact. They want to be close because the electromagnetic force brings them together, but at those length scales nuclear strong and weak forces come into play and at some point overpower the electromagnetic attraction.

This by itself doesn’t explain the quantized energy levels an electron can have or what that probability distribution looks like, others have answered that question better, but this is why the electron doesn’t just “fall in” to the nucleus.