Because for anyone who (still) actively uses faucets, the new reCAPTCHA is much more difficult / time-consuming (if it's one of those "select all things until none are left") to fill in (probably due to the high volume of captchas filled on the same IP). At least that's what I've seen some users complain about. In addition, sometimes it's difficult to tell what specifically the captcha is asking you to mark (e.g. do the poles on road signs count as part of the sign?).

That aside, since it's important to stop bots from bruteforcing passwords, AFAIK the new reCAPTCHA is the impossible for bots to automatically bypass (for now; though if anyone is going to break Google's new captcha, it's probably going to be them - hell, that's why they created this new one). Gonna be a bit of a pain in the ass creating user based Bitcointalk bots / libraries though (not exactly a fan of manually requesting keys for each bot but I guess I've got no choice until this gets resolved (fingers crossed for the new forum software modular API access)).

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Here's an example of the "select all things until none are left" captcha slowdown (that I've encountered personally as well):