A change to StackExchange's policy towards beta sites was announced earlier this year:
Community Managers haven't posted here (on this site), and I don't know whether they still try to judge sites as they used to, but here FYI is a Community Manager's posting on another site (CodeReview.SE in 2013) before it graduated ...
... and here are some follow-up topics which show how the CodeReview.SE community responded to that feedback ...
Note this answer especially.
One of the things Grace said was that a graduated site site shouldn't have too many low-reputation users. If I recall correctly, the more low-reputation users and the more traffic it has, the more high-reputation users it should also have.
The meanings of reputation levels change when a site graduates, for example compare Buddhism's (in beta) with Code Review's (graduated).
One of the metrics to consider (i.e. which community managers either still consider, or which they used to consider) is the number of users with a reputation of over 3000 ... because that's the reputation required to cast close votes when the site is graduated (currently equivalent to 500 on a beta site). I think they assume that on a busy, graduated site there will be off-topic and duplicate questions which need closing, and that there should be a community (of several active users with a reputation over 3000) who will do that, without relying on the moderators to do it.