I know the Beta badge description states:
Actively participated in the private beta
However, what constitutes "Actively"?
I'm not saying there is anything wrong with the 91 awarded, it just seems too few given the statistics on Area 51.
As mentioned here on meta.stackoverflow.com, the exact criteria is hidden to prevent people from merely doing the minimum amount to get the badge:
silver; awarded once
Participate actively in a site's private beta phase
- Not just 3 bronze badges anymore, but the exact requirements not disclosed to prevent users from just doing the bare minimum. (source)
Not awarded on Meta sites, including Meta Stack Overflow