We can finally put the Jaylen Brown doesn't want to stay in Boston rumors to rest now. The trade kicker is the nail in the coffin.
Personally, I don't view the trade kicker that way, rather I see it as more of a control element for the player: "I can waive the trade kicker to help go to a team I want or will at least be compensated if I get sent to a team I don't want to go to." Just like a no trade clause, it didn't mean Bradley Beal really wanted to stay with the Wizards, he just wanted to be able to control where he could go.
And I'm probably more cynical about these things in general (happy Jaylen signed and is locked up though), but one of the reasons I'm not as bothered by guys like Harden and Lillard and Durant demanding trades is I believe there's often an unofficial handshake agreement between players and teams when signing these max contracts, "sign with us, and if you decide you want out in a few years, we'll do our best to move you where you want to go." Like I'm pretty sure this is exactly what happened with Paul George and OKC. And not saying Lillard, Harden, Durant, etc. handled their situations well, but I would bet they were all told something similar at some point, so it's not really as clean as the "well you shouldn't have signed a 5 year max contract then" argument people make.