To be an alliance leader you have to be committed to a great degree. And firm but fair. Most active alliances will have a few players who will help the leader identify inactive members, and the leader must act on those who don’t contribute.
Thee are three types of alliance. The very keen and active type who insist on members joining discord or something similar, where you post evidence of your activity, and sanctuary building is discussed.
Then the less dictatorial type that still hits 5/4 but perhaps doesn’t hit high sanctuary targets, and has a pretty much full active membership. No necessity to join discord or prove activity, others than trophies.
And finally the alliances who accept pretty much anyone, have half of the members on zero trophies and don’t really get much of anything every week.
Each type has its merits, and everyone’s playing style will suit one or another. But one thing is for sure - it isn’t fair on active players in an alliance to be carrying people who dip in and out and don’t really contribute. Leaders have a responsibility to tweak out the dross if they want a good alliance. Ludia don’t help as tools aren’t there to help, so a message in chat and keeping an eye on trophies is the only real option.