Because you're making people jump through hoops and put their identity on the line just to sign up and post on a forum, a forum where most people value their privacy or wish to remain anon for whatever reasons. Most people tend to think the newb time restrictions and previous newbie jail are bad enough without adding more complications to just signing up in the first place.
Bitcoin is not anonymous. So why is Bitcointalk trying to be anonymous? The admins also never said alts are allowed because of anonymity. The reason given is difficulty in enforcement.
As for jumping hoops. I would argue legitimate and honest users are asked to jump through more hoops to navigate through the scammy minefield here.
If you really want to talk about hoops, the six minute posting requirement for newbie accounts is the biggest hoop around.