dude I've been wondering the same thing for a while but the problem is, they need to do this or they're useless to the meta, they aren't quite as tanky as tanks and they don't do as much damage as squishies (hard to believe sometimes but it's mostly true) and they're also very mobile
problem is being about 65% of the damage and tank while technically 130% of a champion is 200% of a mess that can't do really anything well and they're forced to either abuse tank items with base damages or go full ad because of their stupid scalings. and they only somewhat fall off lategame, because while they don't have the intrinsic cc of a tank they do have a hefty amount of damage they can dumpster onto a single champion which is more than enough reason to sic 3+ people on them to keep the high priority target alive which = win for the bruiser or have it taken out which also = win for the bruiser. I actually like jarvan's concept if not his damage, he has a lot of cc in burst but it's not sustained and some tank for himself, making a great and scary initiator against multiple targets. unfortunately his bases and scalings are so good he can literally take a single ad item and with not even 200 ad delete one to several people off the map even if they are relatively tanky because his passive also scales on %hp and his flag gives him good dps.
I didn't have much of a point or a solution, just more gripes about bruisers as a support main needing to keep these tumbling tumbleweeds of shit off of my carries with little to no success usually.