Unfortunately, I think a big piece that has created such high expectations from the parents is the fact that they are heavily financially invested in the program.
Back in the day, HS sports were like "advanced" PE. They didn't invite parents to preseason meetings and ask for support. Just another class in the parents eyes. No one would ever go to their sons PE coach and ask why is my kid not getting in better shape. Parents hardly spent a dime on their kids for sports. Maybe an occasional glove, cleats, or bat, but that's it!
Today parents have had to fund sports from the get go. With a lot more expenses than years past. Which include everything from private lessons to travel and annual gear for multiple teams from head to toe.
Heck in LL when I was kid, if you should up to practice in uniform YOU were the dork! Jeans, T-shirt , and hat was the norm at practice. As a dad I was shocked the first time we went to t-ball and every kid was equipped like a pro. Multiple gloves, bats, matching helmets, full on uniform, and etc... I was shocked and quickly conformed to burning $300 a season in BS equipment.
Get to HS and all the sports programs are begging for money. Rich programs with what I consider close to college level facility and equipment.
Of course, a HS program asks for support from parents they are going to get it. The more support they ask for the more they will get. Unfortunately some of the support will not be in the coaches favor.