There are two types of cab drivers: those who talk to you from the moment you get into the car and those who don't say a word, even if you strike up a conversation with them.
I'm the kind of person who doesn't really mind talking to a cabbie. I'd imagine that passing the time while driving around all day can be a challenge. And if you're transporting humans to different for hours on end, I'd like to think that you generally like people.
That being said, I totally get people who would prefer that their cab driver stay completely silent, because almost every single one of us has had a strange interaction with a driver who's been a total weirdo.