Why are all other planets, stars, and moons in our solar system and our galaxy spherical?
Do you have any evidence for these claims?
Well, you can check this yourself for Mars and Venus with a telescope that isn't too expensive. And if you buy a decent backyard telescope you can confirm it quite well for Mars. You'll need to be patient and you will need to do it somewhere without much light pollution but this isn't that tough for at least those two bodies. Detecting the roundness of other bodies is tougher (incidentally Lagnaf is actually incorrect when it comes to moons. Some of the smaller moons are not spherical (such as Deimos and Phobos, the moons of Mars). But even detecting those bodies is very difficult since they are so small. (This is precisely why they aren't spherical- you get near spheres when objects have enough gravity to pull themselves into a spherical shape. That's why all large objects are sphere.) They weren't detected until the late 19th century.) So you can't see them with a small telescope.