What are the parameters which are taken into consideration when deciding that a certain site is needed?
Have a look at the proposals within the Area 51 site for the site you want to know the answer to your question.
As a sample, go check it out for DevOps.SE. The beta-tab shows the current status (progress), indicating what is still needed for the site to become mature enough to "graduate" (= change from beta status to no-longer-beta).
Even though there appear to be exceptions, as soon as all 5 indicators have changed to Excellent, additional steps are taken to actually obsolete the beta status of the site, which may still take a few months or so.
PS: with the above in mind, if you want to help DevOps.SE to graduate, just try to post some more (good!) questions, and / or try to answer existing questions.