Part of being a successful Mole is fooling as many players as possible. The thing about casting Craig as the Mole is the almost certainty that at least half the cast would pass him off as the Mole due to his weight. I'm pretty sure that's why Marcie stuck him outside with Liz, Bobby, and Nicole because she didn't need to spend time with him since she figured he wasn't the Mole.

By the time people started figuring it out, there would only be a few people left and that's when you want some people to figure it out.

If he is the Mole, he's fooled everyone up to at least Alex, so I guess it was a clever choice. I do have to give him credit for blatantly misleading people he liked like Bobby and Victoria.