!Friendly had many problems.
The most major one being after the GunMettal Update regarding weapon drops. Where the player could pick up weapons and kill other players essentially having Godmode. The first fix was to remove weapon drops completely.
But then if you wanted to inspect someone else's weapon, you'd have to spectate for them, and lose chance on the biggest installment gameplay to TF2 Since new weapons.
For what made the final decision I'm unsure of, but !friendly contained far too many flaws as a pluggin, and cannot be easily fixed throughout its many bugs and conflicts it contained.