If the library is alive and mature but there are not many users, then something is smelly. Why don't people use the library if it is good? If the number of users for a library or framework is low and there are no large corporations among the users, then it is probably not a good one. Nobody using it may signal that our assessment of the other criteria may not be appropriate.

Also note that if there are only a few users of the library, then the knowledge in the community is also scarce and we may not be able to get community support.