Why didn't most people in Europe buy African slaves?

It was against their religion.

European explorers didn't go to Africa.

They had enough cheap labor.

They had Native American slaves.

I'd pick the third one down. Europe was more advanced than (say) Brazil and the southern United States. Europeans needed a trained labor force and that's what they strived for. Brazil may have had many slaves, but they had a problem with disease like Typhoid fever. It does not take much to learn how to harvest crops. It takes more to learn how to properly manufacture something.

I'll stick with cheap labor, but you have to realize that slavery even now was practiced in some European small and Asian countries.