The thing is though, they don't get big money just because they've been on the air for over 25 years. They get paid because it turns out, there are some god damn talented voice actors that voice your favorite yellow skinned Springfieldians.
All it takes is one picture to show you:
|Dan Castellaneta doing Santa's Little Helper is the best.|
Over one hundred characters in The Simpsons are voiced by twelve very talented people—and here's a breakdown of who does what.
The image, which comes from @Jishai, might not be a surprise for hardcore Simpsons fans, but it's still fun to see everything laid out like this. Speaking as one of those, it is not, but man is it good to have to settle all those late night Simpsons voice actor assignment conversations I have had.
Compare to the cast of South Park, which is primarily voiced by four people:
|Trey gets all the good characters....|
Dan Castallaneta and Trey Parker are gettin' it.