It's about both. The USTA does not own the courts used for league play. It is very important to be respectful of the entities who own the courts. Some areas may have large public facilities that have plenty of courts for league use and no restrictions, but some areas do not. League administrators have to balance the needs of the players and the needs of the facilities. If the leagues/players are being too demanding, the facilities can simply do away with USTA league play. If you owned a facility that had tennis courts and an outside entity told you how to operate and demanded unlimited court space, I doubt you'd appreciate it. Most facility owners appreciate the fact that adult league play does bring in memberships, court fees, lessons, pro shop sales, etc. But that doesn't mean that they don't also need court space for their own events, lessons, youth programs, etc.
League administration is not easy. A lot goes into and league players have little appreciation for it. The fact that you are getting surveys is good and means you are being listened to. But other things factor into decisions. Sadly, many players have a very narrow view of leagues, and think that every area is just like theirs. Their expectations are simply not in line with reality.
To all the singles players who want more singles play, why don't some of you start your own singles league?