Granted that's outrageous (one reason I don't go to ballgames) but nevertheless, the parks are filled. Who then is going to the games? Just the rich? I doubt it. I'll assume that most of the fans are non-rich. And if people are willing to pay those crazy prices, the clubs are quite happy to charge them the limit.
But going to a ballgame is hardly a necessity. And the facts are the cost of feeding, clothing, and sheltering a family are a lot less than 30-50 years ago. Candy bars are also a lot higher, but they're hardly a staple food.
So even though it's a near-monopoly product, even the Cubs understand that the quality of their product does not match the market demand for tickets to see it.