They might look that way and may galaxy typers are flat.
On common perhaps most common galaxy type is “dwarf spheroidal galaxies” that are sphere.
The will look quite flat if you see them but that is because you only see them from one direction.
You tell a sphere and disc apart by looking how ligh illuminte it, how it cahgnes when it moves. But if you buld a sphere or disk with lightsources like a galaxy you can exacty tell them apart.
https://physics.stackexchange.com/questions/148418/why-arent-there-spherical-galaxies/148533
Everything in the universe is spinning, including galaxies. Galaxies start out as big spheres of gas. All those particles are orbiting around the center of the sphere. Some of them might be orbiting almost vertically, while others are orbiting more horizontally. Over a very, very long period of time, these particles crash into each other, and when they do, they cancel out the different directions that they were going in and start going in the same direction (conservation of angular momentum). So eventually, most of the things in the galaxy end up going in the same direction, because the stuff going in different directions crashes into each other.
Imagine a spherical ball of gas and dust, where each individual particle is traveling on a circular orbit at some random angle relative to all others. Sometimes, the particles will collide or interact, and the result will be that they lose some energy along their path, or even stick together. If they collide head on, the motion of one can basically cancel out the motion of the other, and those particles functionally stop orbiting. They’ll fall to the centre of the cloud. If the cloud is dense enough, most of them will do this.
But what if the orbits aren’t totally random? What if the majority of the particles have some component of their motion spinning around in the same direction? Well, then when the particles collide, their orbits won’t totally cancel. The “up” and “down” parts of the orbits will, but the sideways components will add up… The result is, over time, the cloud will collapse down into a disk, spinning in the direction of the slight overall spin of the cloud.
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