There are so many knockups and displacements in the game and there is no counter to any of it.
can prevent any displacement effect in the game from happening.
reduces the effect and duration of all knockups and displacement abilities by 50%
This would neuter a wide range of knockback/pull/fling skills, rendering champions that rely heavily on them obsolete.
Also: True Damage and Invulnerability exist in LoL.
Displacement is the equivalent to such powerful effects on the CC side of things. Some champions need consistent damage to function, some consistent defense, some consistent CC.