Garp disrespect CDs and does other stuff not allowed too
We learnt from Sengoku that they can't punish or kick him out cause of his heroics and might
They were never gonna punish Fujitora unless he attacks Gorosei/Imu directly in a fight
Garp was never an admiral which means he was never directly under CD thumb. GB(an admiral who is directly under CD thumb) was threatened with a death sentence if any CD got hurt.
In MF aftermath, the WG wanted to keep the ID break-in under wraps and Sengoku couldn't do shit about that.
If a CD ever ordered an Admiral to be executed, it will undoubtedly happen.
The problem is Admirals are too strong to put on death sentence even by the WG. The only people who could possibly do is Imu.