What's the Deal with Voice Talent?

It is kind of unexpected when you come across a company who has an ad out there and who clearly didn't sign up the right voice talent. You speculate what the deal is, why would they not take the time to sign up someone to do an efficient job? They take the time and money of making an ad, they pay for the radio air time, yet their voice over individual just does not seem to get what the product is about. They don't sound believable when they are talking about the product and they do not inspire excitement either.