According to the same rules that govern free agency in sports, our super heroes have the right to sell their services to the highest bidders. The major markets will have the best, and the smaller and less attractive places will have the leftovers.
Now, in terms of super villains, they really can’t be top tier unless their main nemesis is a top tier super hero. Sure, it’s tougher, but the exposure and money is going to be markedly better.
The exposure, sure. But the money? I find that questionable.
This makes me wonder if there is a hidden tier of criminals in the DC universe. There’s the low level crooks who commit street crimes; they’re the ones who routinely get punched and rounded up for jail. Then there’s the high level super villains; their goal (never fulfilled) is to fight and defeat a superhero while wearing a brightly colored costume.
But there’s probably an unseen middle level of professional criminals. Their goal is to make money while avoiding the attention of superheroes.
Endorsements. 
They worked for Captain Amazing.
Until they got a cease and desist letter from the real Avengers. Then they realized that all of them were mutants, and started calling themselves the Great Lakes X-Men.
Until they got a cease and desist letter from the real X-Men, and they became the Great Lakes Champions.
Until they got a cease and desist letter…