Not meaning to sound sarcastic by any means, but I think the fact that all of them are significantly younger, and would come on a cheap rookie contract for the next 4-5 years would be pretty decent reasons.
With Mallett, yes-- you're getting someone with more "experience" (and I use that term loosely), but you're also getting someone who needs to re-sign a brand new deal at the end of the year that you're going to have to take a big chance on financially, and someone who's about 5 years older than some of these guys.
Those reasons may offset any value that someone may see in Mallett. Of course, there are also the potential pluses that you speak of as well, so it's all about if someone wants to take a chance on him or not.