Why Do So Many Damage Items Have Health?

AP: Liandry's Torment, Hextech GLP, Hextech Protobelt, Rod of Ages, Rylai's Crystal Scepter

AD: Frozen Mallet, Black Cleaver, Titanic Hydra, and Trinity Force

It doesn't really seem like a lot of items(which would make sense because there shouldn't be that many damage items that also make you tanky), however pretty much all of them except frozen mallet and hextech glp are built on SO many champions. Champions with % max hp damage(cough tanks) just seem so strong right now. It is weird to see an ap mage walking around with lyandries, rylais, and rod of ages and have so much hp (1100 bonus hp). This is great for Fiora, Vayne, and even tanks who have % max hp in their kit, but it gets really annoying when you are playing gangplank, jhin, and other champions that are meant for ranged burst. They tend to be fairly immobile and just get one shot by the midlaners/bruisers that they cannot kill.

Earlier, I was playing a game as gangplank and had to lane against an Illaoi. The lane went okay and we were about even. By the time i finished TriForce and Youmuus I was doing around 400 damage with my barrel combos...the problem was...no matter how many of these I landed...I wouldn't make much of a dent in her hp even though she had next to no armor(her build at that point was black cleaver + steraks).

Just wanted to ask what others think about this because a lot of damage champions feel way too tanky (I am noticing this a lot after I starting learning Gangplank when I normally play Fiora).