According to the answer What are the success criteria for an Area 51 beta site? when the site after 90 days in beta becomes eligible for graduation as a full site, it will be launched. However, most of the sites don't fullfill this criteria in 90 days.
Then it is written:
If the site has not reached these goals by 90 days in beta, it can remain a beta site as long as it continues to show steady progress. But if the beta site is showing a general, unrecoverable, downward trend, it may be closed as inviable.
From that I could understant that the site that failed to fullfill that criteria in 90 days, can be trapped in public beta forever. And once in falls in downward trend, it can be closed.
Take an example: Personal Finance and Money
It stays in beta for almost 2 years, have all goals to excellent, only number of questions is good (5,1 a day). OK, everything could be excelent, but:
Role-playing Games were started, and it have much worse statistics in the start moment. The number of questions per day was 3,4, with status Needs work.
From the following examples, I see no rule, when the site trapped in public beta phase will be started (or if it will be started).
So, please, could you say, why Role-playing Games stared, and why Personal Finance and Money has not, and what criteria would be taken into accout to start other betas, such as Travel etc.?