As I understand it, voice actors in the US are paid relatively poorly, so it’s not a career that many people aspire to. Most actors prefer to do live-action work, because it is paid much better. The ones that aren’t talented enough to do the live-action roles are left to do voice acting. (That’s not to say they’re all talentless, of course! However, there is only a small pool of quality voice actors, like Tress Macneille, Dan Castellaneta and Jim Cummings, and they are in very high demand.)
And within voice acting, dubbing over a foreign film or TV show pays less than acting in a US-made animation. Most dubs are done as cheap as possible, because there’s not much of a market for them (with the exception of big-name stuff, such as Disney’s dubs of the Studio Ghibli films).
So basically, dubbing foreign films and TV into English pays peanuts, so only the crappiest actors take that sort of work.
It’s a different story countries like Germany, where the actors who dub over Hollywood films are household names, and presumably much-better paid.