Since kryptonians know that going to earth can make them superman, why don't they all come to earth?

Actually, if you go to African countries, they are particularly backward. Your ideas and skills, relative to the African primitive black, you are completely superman.

Now the question comes, why don't you emigrate to Africa?

superhuman beings are unwilling to move to the earth, and the principle is the same.

As we all know, the natural environment of Krypton is much worse than that of the earth. The stars of the earth are younger and brighter than that of Krypton, and the cells of Krypton people absorb its radiation, which strengthens the skin and muscles of the senses. Moreover, the gravity of the earth is smaller than that of Krypton, and its air can nourish people more.

Superman is different from other Kryptonians. Why don't all Kryptonians come to Earth?

kryptonian has been blown up, where are the other kryptonians? Later, other superhuman beings were different in space or timeline.

Superman also has super powers on his own planet. Yellow sunshine only strengthens him. Look at the kryptonian city that Brenyak took away. It can fly.