At a guess, because crowd control breaks their encounter design and instead of improving their AI or their design, they just nerfhammer the things that break their encounters too much.
It's the same thing with ranger familiars and mage hand. Having infinite 1 health rats or hands could be abused so they just made the summon once per rest and left it at that. Fixed the problem with encounter abuse, but now those abilities don't really do what they're supposed to do, and the character concepts that relied on those abilities doing what they're supposed to are consequently hurting.
But at least Larian can count the stacks and stacks of green, as they sit quietly in their ivory tower fortress in Ghent.
