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

No answer for you, but I think what you’re looking for is planar movement. Or why the planets orbit roughly on the same plane in 3d space. Not “horizontally”