See why here.
The author cites some very good reasons why liberal think tanks will fail, which I appreciate. However, the simplest explanation is that the Liberal agenda no longer produces or encourages "thinking". On the contrary, the leaders of the Left simply require a worshipful obeisance of those old ideas from the 30's and 40's. To consider changing or improving them based on rational thought is considered "haraam." (to use a religious term).
Liberalism is a religion now, and its followers must accept it and defend it on faith. Usually they are too busy chastising the Christian community to notice that they treat their own ideas as holy and sacrosanct relics that are above scrutiny. criticism and intelligent discussion.
Liberals critiquing their ideology are about as common as Saudi imams dissing the Koran.