[colechristensen]

It seems there are several things going on. Protons absorbing electrons becoming neutrons doing the opposite of decay, a sort of connective cycle that radiates away neutrinos while enabling decay and reverse decay, and plain old Pauli exclusion where there is no room for electrons.

But it all comes down to lots of things being possible in such a crowded place and neutrons not being “free” in a neutron star. Nuclear chemistry is full of crazy stuff happening constantly in stable situations that all kind of balances out.