Is this just a meta thing, or are knock ups just too good?
In most cases I wouldn't say knockups are too good, they tend to have much shorter durations than other forms of CC in exchange for being the True Damage of CC in the sense you can't counteract them with Cleanse/QSS/Mercurial/Mekael's/Tenacity.
(Just as HP effects flat true damage and %AS slows effect both %max HP true damages to a certain extent, BV does effect knockups).
Most champions that have knockups also rely heavily on their CC doing work for their kit to function.
Course, there's always champions like
that have a really powerful knockup because reasons.