I don't think the time and money commitment to travel ball, be it soccer, baseball, basketball, etc is as much a reason as being made here. Sure, it does take time and money, but it isn't a deal breaker in most cases.
IMO, the real culprit is that kids stay in the house more and don't congregate in the summer at the baseball fields, basketball courts and just play! Be it due to kids being at a daycare as both parents (if there are 2 in the home) are working, not allowing the kids to run their neighborhood or just staying in the house playing video games. I truly think this is why participation in sports is down.
Sports are accessible to play....all of the schools that I know of have baseball fields, basketball courts and greenspace that kids can congregate on. No need to have sponsors, schedules or team booster clubs..just kids who want to play.