My son stopped bowling in Sat morn leagues 4 years ago at age 11. Not enough competition for him. We've been traveling every weekend to tournaments in other states. The only serious league he has bowled in the past year was a PBA league which had a major influence in him improving so much at JG last year. Having said all this, I would have to admit that I appear to be the exception more than the rule. Most parents can't or won't make this kind of committment. I saw early on my son's potential and decided if he wanted to do it, I would support him to whatever extent possible.
The question I would have for the other parents in your league who made that comment is,"why should the serious, successful bowlers suffer at getting better just because the others see it as recreation or a baby sitting service?" I would try to have the center put out a shot for them either in league or after so they can improve.......but that's assuming it doesn't interfere with their ever profitable birthday parties.