The answer is right in front of us. All these things mentioned by you and others are due to electricity. Atoms, planets, clusters of galaxies.... all work on the same principle. It is what caused the bits and pieces of the early universe to 'clump' together. A scientist has already discovered this 'clumping' effect, which surprised everyone. He was just experimenting while on the Space Station, and wasn't trying to find this particular answer.
The movement of everything in the Universe alters the balance of the electrical charge of the material in the Universe, causing it to attract or repel other material. The electrical 'potential' is like water. It will seek the lowest point. Electricity seeks a perfect BALANCE (net charge of zero). Which we don't want, because if it happens, nothing will exist.
In that most things are not in perfect balance, there is a constant exchange of charged particles, and this is what comprises the electromagnetic spectrum, and enables the Universe to exist.
We do know why mass, charged particles do the things they do, we just don't know how.
Magnetism, gravity, the force that keeps electrons in orbit around a nucleus... All of them move another object from a distance, without any physical contact. That violates our physics rules.
correction: “and enables the Universe to (continue to ) exist.