I thought that leagues were sort of their own separate thing for a while, until I started comparing pool to a lot of other sports/games. Leagues get people involved and almost all of them are enjoying themselves, whether or not they're any good, while contributing to the base growth of pool. Leagues are in virtually every major game or sport. People look forward to see how their favorite teams and players are doing. The more that people are involved, the more people want to be involved.
Whether or not their level of play is 'acceptable' to others has no bearing on that fact, just as pretty much every fan of every sport has about a .00001% chance of actually being worthy of playing along side those that they watch. Leagues are also a huge benefit to pool halls and pool bars. (Going to check online for some numbers real quick...)
The summer session is usually a little less busy, certainly due to Portland's lack of nice days for, well, the rest of the year. Only making note of a few places out of very many, I've got a few numbers for you:
Sam's Billiards(Pool Hall) - 11 APA teams, 5 of which play on a Tuesday.
River Roadhouse - 7 teams
Fortune Star - 12 teams, 6 of which play on a Tuesday.
If I read it correctly, there are 32 divisions for the summer session, not including the extra double-jeopardy sides for some of them, since they are the same people. Playing both 8b and 9b does mean that teams are usually around the place for a little while longer, because if one does end up getting done early, chances are the other will finish at the usual time.
Ask yourself, how many of those people do you think would go out to a pool hall regularly if not on a team? Probably half at best, I'd guess.
Fortune Star has 6 diamond barboxes for 6 double-jeopardy(8b & 9b) teams. Half of the teams play away, while the other half host. That translates to a minimum of 5 players on each team times 6 teams. You've now got 30 more bodies in the building each Tuesday night, or up to 48(8x6). I'd put money down that just about any pool hall or pool bar would be drooling over those numbers, even if only half of them spent money.
Get people out, get people involed and you'll have places looking to cater to those numbers. It seems any place that gets diamond tables around here suddenly gets multiple teams. If people want money put into pool, they need to give people a reason to want them around. Pool leagues can help accomplish that. Anybody that puts them down as a hinderance to pool is either arrogant, ignorant or trying to fool themselves. As I mentioned before, higher level leagues make it even better, as people also have something to look forward to. Pro leagues should be high-dollar, and you may get some extra people in them just to play those top amatures, shortstops and pros.