Gravitationally bound objects are elleptical if they have low friction (due to extremely low gas density between compact objects) like elliptic galaxies, oort clouds, and many other things, or are supported by pressure like stars, planets, and big satellites. They get more spherical if the angular momenta of each of their constituents are more equally distributed (only for low friction objects. High friction objects supported by pressure have an angular momentum in a specific direction) and if they are less disturbed by the gravitation of nearby objects.

They are flat disk if they have high friction (due to high gas density between compact objects) and are supported by angular momentum., like spiral galaxy, planet disks and accretion disks. They remain flat until perturbed by a collision even if the gas density went down enough that the friction is now low. That's the case of many planet disk and spiral galaxies. After a collision, they will get first irregular and then elliptical.

The accretion disk around the sun used to be a high density region while the gas was falling into the sun so it became a disk. Most of the gas and dust fell into the sun, but the remains are the planets and asteroids. The oort cloud is the part of the cloud that formed the sun that never got enough density to become a disk.