Why don’t planets revolve around the sun vertically?

If we imagine a solar system as originating as a vast cloud that slowly condensed and coalesced into a star and orbiting planets, asteroids, and comets, it stands to reason that all of the bodies would orbit in the same general direction because they all are orbiting as part of the angular momentum of the original cloud.

Let’s visualize such a cloud.

We know that angular momentum is conserved. We’re all familiar with seeing an ice skater start rotating slowly with her arms outstretched and then she pulls in her limbs and starts to spin faster. The more she concentrates the space her body takes up, the faster she spins. The same is true for our stellar cloud.

We start with a vast cloud. It has some net angular momentum, causing it to rotate very very slowly in one direction. As gravity causes it to condense, that net momentum becomes more evident because the cloud starts to rotate faster.

The mass starts to concentrate at the center of the cloud, this center mass will become the Sun. The remaining mass orbits the central mass. A small mass orbiting a large mass orbits about the center (well the barycenter, but it’s pretty close). That means we can’t have the material orbiting the cloud like this:

It has to orbit like this:

Now we’re kind of getting to the vertical scenario. This exact scenario isn’t practical because the angular momentum in the pure vertical is zero. But what about out of plane towards vertical.

A system like this can exist - but it will not last - because, the two layers that are tilted have vertical motion components - they will cross through the center layer. That means there will be collisions. Over time these inelastic collisions will dampen out the vertical motion and the result will be every particle in a very thin plane like this:

And, over time the small particles in this plane will coalesce into larger bodies, forming the planets.

Source: Quora