Rather than asking why I suspect the three, I suggest you ask why I don't think this is a good lead.And why do you suspect one of these three people? The difference is that Drac's 50% ability is completely random, while this is not. You can deduce who is probably mafian from the lead... which is what the game is about.
The answer to the first question is already stated: They are substituted.
The answer to the second question is because despite this being a lead, I want a 100% scumlynch. Also, I wouldn't know who to lynch between the three of them. --that is, until MathBlade disappointed my expectations of him.