I have never spoken to anyone at Sporcle HQ about this and they have, smartly, chosen not to weigh in on this thread or the other one. I would venture a guess, however, that Ebert's estate is very protective of his name and his prior reviews. Those prior reviews and his "thumbs up/thumbs down" rating style remain the intellectual property of his estate. IF (and this is just conjecture on my part), there had been a Sporcle quiz that used direct quotes from his reviews, it is entirely possible that the estate's lawyers would contact Sporcle with a cease and desist letter, threatening legal action if any protected information related to him continued to be used. Under that circumstance, it would be wise for any entity to simply refrain from using his information or his name. Overkill? Perhaps. But safe territory none the less. I would note that a search of the name "Ebert" turns up nothing on Sporcle, which would suggest that any quizzes using his reviews have also been removed (again, if there ever were any).
That said, I'm just a volunteer here and can't speak for the business entity that is Sporcle. But as a lawyer, the lack of quizzes and blocking of the name suggest to me that something similar to that may have happened. It would not be at all surprising or out of the normal course of business for Ebert's lawyers to take that action and it would not be at all surprising (and legally prudent) for Sporcle to simply block the name in response. Blocking the name would satisfy the cease and desist terms, protect against future infringement and likely discourage users from violating intellectual property protections in the future.
I would note that the U.S. Copyright office shows 42 copyright applications connected with the name "Roger Ebert" (most of them for his 'Video Yearbook' publication), and the of use of the text of his reviews would be a possible copyright violation. The use of his name would be a trademark violation and the name 'Roger Ebert' is the subject of two separate registered trademarks, one for his name alone and one for RogerEbert.com.
In short- blame it on the lawyers. We're always the cause!