Why is there gravity?

[Alex K]

Yes, in a sense, electrons in some energy level don't have a fixed distance to the nucleus. But strictly speaking there are no such things as electron orbits, there are only wave functions giving you probability of location and momentum. The picture of a pointlike electron orbiting the nucleus is false

Could you then explain in relative layman's terms what "localizing the electrons in a smaller and smaller space near the nucleus automatically lets them have a larger momentum due to the Heisenberg uncertainty principle, which then lets them escape" means?  If the electron as a point particle is a metaphor, then it seems that statement relies heavily on that metaphor.

Nothing relies on metaphors because the actual arguments are maths based. The calculations are performed in a theory framework, which in the case of quantum mechanics assumes electrons to be point particles, but which are subject to quantum uncertainty and whose states are therefore characterized by their wave function. The assumption that the electron is pointlike is a good one because it is empirically tested on the scales relevant to atomic physics

What is meant when one says that the electron is localized in a small space, is that the quantum state of the particle is prepared such that the wave function vanishes outside of this confined area.