I worked at the Fisher Cats' stadium for one summer when I was in college in 2006. Honestly I still don't know how so many teams stay in business now that we have so much saturation in entertainment and you can see everything on YouTube or Netflix, etc.
I suppose there's still a market for live entertainment for families. My parents took us to a couple Sea Dogs games as a kid because we weren't privileged enough to afford Red Sox tickets. But those were Fridays and Saturdays, ans there are so many mid-week Double-A games with like no one in the stadium, I don't know how they stay afloat.