Some people are incredibly stubborn and are very prideful. Aramis may be one of those people. Sure, there's that, but that would also basically require him to be an idiot and completely ignore how he's killing his opportunity to opt out and get a much better contract. And it's not like the guy's never been on the DL before. Not sure why this time it would be an "I don't wanna go on the DL...I'll play injured and play badly instead" situation.