I've worked a lot in the private sector, at hospitals for example, and I there were very specific standards. They could not just fire me. They had to work through the procedures. Even at nursing homes, where aids were often considered a dime a dozen, there were procedures.
As to why it cost so much to fire a teacher, I can see where they're getting their costs from. I would love to see a break down. But I also would blame those who negotiated with them. No law made anyone signing anything that would be that expensive.