I absolutely agree, we do need better AP bruiser items, but I understand why the devs are so hesitant to make it happen.
We've got
. He's pretty much the only true AP bruiser. We've also got
who should by all rights be AP bruisers as well, but the lack of itemization has forced the devs to balance them around being assassins.
We've got a few bruisers who can build AP, but currently build other things because they're hybrid and/or scale with other stats, like

Then we have the tanks, who add another twist to the problem. Lots of tanks scale with AP, so items that give you heath/resistances and AP would need to be balanced around champion like

We also have battlemages like
, who would also want to build AP bruiser items, but their existence means you can't just slap on "melee-only" to keep burst mages and assassins from abusing them.
And that's the main issue here. Champions like
who would love to build AP and health at the same time and never die while dishing out mountains of damage.
They can't just slap an AP version of Black Cleaver in the game and call it good. The lack of AP bruiser itemization is a huge, systemic problem. Giving AP bruisers even one good item would require AP champions across the board to get adjustments so they can make sure it's only the bruisers and tanks that are building those items.