Why do planets orbit at the same level as each other?

Question

By that, I mean, why do planets always orbit… horizontally(?) around the sun. Why not vertically? Space is a 3D space, I’d course. So why would the planets not end up going up as well as sideways?

Edit: Space science is a lot more complicated than I thought, and I am here for this rabbit hole. Ty everyone for your answers so far!

In: 2352

Answer 1

A spinning object has more speed at the equator than at the poles and therefore can throw bits and pieces farther. Sun is such spinning object and planets have formed from “splashes” from it. This video demonstrates the physics pretty well: https://www.youtube.com/watch?v=FVo2qdXxQ7o