Why would a voice actor be any better than professional sports commentators who work for major broadcasting companies? If anything, voice actors could be worse seeing as they may or may not be as familiar with the subject matter.
Availability. A professional voice actor can give more time to a project than a professional announcer who gets a lot of work and has a lot of obligations.
Generally speaking, an on-air personality has to hold onto a certain demographic to succeed. I don't listen much to commercial radio but I would think that a person on radio needs to communicate clearly, intelligently, humorously, genuinely. And to have some facility with language and a good understanding of interesting topics