I also think it's not about sympathy commit.
The main cause could be lot of desilusionsdisillusion and disapointementdisapointment.
I commitedcommitted to a few area51Area 51 proposals bywith real interest and passion (yes including this one), and all sites that went to beta phase did not meet my expectations. The saddest example is audio.stackexchange.comhttp://audio.stackexchange.com that will probably die soon with it's 215 questions.
Maybe we should be more strict with requirements by increasing the number of commitedcommitted users and examplesexample questions needed to enter in beta phase.