This is my speculation on why Big Boss wants TJ dead. I think it started out with TJ breaking off the engagement with his daughter. Basically, not giving him face. But that's just a small part of it. I think they wanted an obedient dog that will come when call and jump when asked to. TJ was gaining too much power and influence. Especially with the other gangs in the coalition. So they were weary of TJ climbing the ranks too fast and not someone they can control in the long run. Big boss is old af. So it wouldn't be long before he'd need to step down, but if TJ married his daughter he would someone he's able to control in from the shadows. But since he couldn't control TJ, he decided to get rid of him instead.