>Why do electrons not fall into the nucleus?

It's always possible most of them already have done so :0

Seems to me the positive & negative charges would neutralize, and it would no longer be "matter" as we know it.

Not anti-matter, just not actual matter by any stretch of the imagination.

Which is what most of the universe actually consists of, not actual matter.

Matter itself is extremely rare, few, and far between.

Could be all there is left and can be perceived by those composed of it, are the things that can have a physical nature simply because their electrons haven't collapsed into the nucleii.

Yet.