Simplified: A black hole is the result of density – how much mass you cram into how little space. If something is heavy enough, even light passing near it gets pulled in and swallowed, so there's some area where no light escapes: a black hole.

The difficulty is that you need a lot of gravity to bend the course of light. Gravity gets stronger the closer you get to the center, so at a certain distance, it will be strong enough no matter how little mass the object has.

But most objects are simply too large: Light will bounce off without ever getting that close to the center. You'd need to squeeze them together real hard to make them small enough, but there are other forces trying to keep them in shape that will resist you.

What you mean with "a whole lot of stuff" is the way more stable black holes work in space: A bunch of stuff so heavy that its own gravity is stronger than the forces trying to keep shape. If it's strong enough, it can pull itself together so close that it gets smaller than that distance. Thus, there's now an area around it where light can be trapped.

If you involve quantum physics, things get fucky, and supposedly there actually is some radiation still escaping, which is what the other post referred to, but I'm out of my depth there. There are also different types of black holes with their own complications, a bunch of details I skipped and a lot more I don't even know.

Space is awesome and big and full of nothing and tons of tiny, really fascinating bits of not-nothing sprinkled in, and we could spend our entire lives studying it and never know just how much we don't.

The idea is that the tiny black holes are planck scale and they evaporate before they get anywhere near each other. Picture this:

It takes 10^20 Planck lengths to equal the diameter of a proton. It takes 10^20 protons to equal the diameter of the earth. And it takes 10^20 earths to equal the diameter of the observable universe.