I've never applied to YC, so maybe I'm not qualified to comment, but I'm not sure your remark fairly characterizes what's going on. It seems to me that if YC gets hundreds and hundreds of applications, and if most founders who are accepted say yes, and if people know the situation going in to the interview (which they clearly do), then it's just not worth YC's time to futz around dealing with the few people who can't decide immediately.

Now, if YC and all their clones could agree to a similar cycle, so that founders could pick between different offers, then I would say that YC were the bad guys. But that's not the case (yet).