Again, think like a liability lawyer. Or peacedog. Think like him.
Lawyers do not like messy, when a clean, streamlined option exists.
So, two words for you: class action.
A lawyer can group 5-10 CTE sufferers or the estates of deceased CTE sufferers into a single class action suit worth hundreds of millions if not billions of dollars. Such a suit also remains open-ended and allows other plaintiffs to join and increase the ask. Such a suit can be targeted at a single entity.
That option is not available for suing municipalities and high schools. The NFL is a single target, and a single target with tremendous financial resources.
So that’s why.
More reasons why would include the idea that the league’s lack of a concussion policy makes it an easier path to a winning lawsuit/settlement based upon OSHA standards, since, again, that’s a single standard for workplace health. If an employer in the US is paying a person to perform a service under contract, there are applications within federal law that imply a contractual obligation for the employer to inform employees of all risks and their extent, whether the contract states that explicitly or not.
High schools can argue that the players are smaller, the contact not as great, the players are essentially volunteering to play, etc. Yes, it’s school-sanctioned, but the lack of pay and the lack of contract creates more work for a plaintiffs lawyer than the NFL does.
Thus, to take on the NCAA or high schools, it boils down to this: more complications, less money. Why do that when you can throw a harpoon at the great white whale?
As peacedog notes, there will be other suits against smaller institutions. High schools, colleges, peewee football. The suit against the NFL will be the big dog, however.