Nickpicking On Major Leagues Baseball's No-Trade-Clause

I don't understand why MLB has a No-Trade-Clause on certain players and then try to trade them but have to require an "ok" from the player. i honestly don't understand why that even exists,because around 2 years after they signed the player and he has a no trade clause, and the team wants to trade him they cant. The teams shouldnt offer players No-Trade-Clause Because they dont know what their situation can be years after they signed the player. They might have no choice but to try and trade that player or feel like they can find better value for the player.