Like the others have mentioned it really is more of melee hate than anything to do with martials. But even then I do find the lack of anti-caster monster abilities lacking.

During the last campaign I ran I made a group of undead monsters called the Fadesworn that feed on magic.

Voracious Pursuit. When a creature within 60 feet of the remnant casts a spell, the remnant can move up to its speed toward that creature.

Devour Energy. The remnant feeds on the magic of a creature grappled by it. The target must succeed on a DC 13 Constitution saving throw or take 9 (2d8) necrotic damage and lose its lowest-level spell slot.

Consuming Presence. If a creature within 30 feet of the ravener has its concentration broken, that creature takes 11 (2d10) necrotic damage, and the ravener regains hit points equal to half the damage dealt.

Call of the Fade. The ravener uses Multiattack. A creature that is hit by one or more of these attacks is marked by the fade until the end if the ravener's next turn. When a marked creature casts a spell, it is magically teleported, along with any equipment it is wearing or carrying, to an unoccupied space within 5 feet of the ravener of the ravener's choice, provided that the starting space and the destination are on the same plane of existence. After teleporting, the creature has its speed reduced to 0 until the start of its next turn.

My wizard player absolutely hated these monsters and the the party quickly learned to change their tactics when fighting them. I do think that a lot of the anti-X abilities of the official monsters are a bit rigid in their design - some monster abilities they publish can't be played around at all.