Among all the other reasons people listed, its also because they suffer from extreme crabs in the bucket mentalities.

They absolutely hate to see each other succeed and will sabotage themselves constantly to make sure no one else gets better than they have. From top to bottom of the stack, they pull everyone down with them.

If a black guy starts a business anywhere near other blacks, it'll get looted and destroyed by his own people. If he gets a job, his girl will get fucked while he is gone and his buddy will flex the 1000$ he made selling drugs while his buddy was "acting white."

Every other group is capable of running small communities of parallel societies within other countries. They may be shitty little places, but you can have a Chinatown or Mexican ghetto in town that has its own stores and systems in place. Whereas blacks live in ghettos that are only capable of living because of the government propping it up, while they have to go out and interact with other races to get their daily bread.