I think it's an issue all sides would prefer not to go nuclear. I imagine it could open up the team/league to lawsuits and they don't wanna pay out $400 million plus in "future career earnings" claims.
Kawhi is medically cleared by a doctor paid to look out for the best interests of the team, not the best interests of Kawhi. Dude still felt pain, something wasn't right, got a second opinion from an independent doctor. Second doctor says no you are not cleared you obviously can't play and here's what's wrong with a plan to fix it.
Fresh in Kawhi's mind is what he is seeing every day where teams look out for themselves not their players: the big one around the league is Isaiah Thomas who might've gotten a MAX contract but instead will be paying for a couple million, but closer to home is Kawhi watching Ginoboli everyday go through "the same" quad injury and hobble around without any oh his explosion where the team said he was just fine.