ADD DAMAGE DEBUFF PASSIVES TO TANK ITEMS!
Creating a group of items that all do the same thing is assuming that all the champs who use said items do the same thing. This is inherently untrue of tanks.
Tanks and Tanky champs have a diverse range of playstyles, Sejuani is completely different to Ramus, who is completely different to Malphite, who is completely different to Shyvana ect. Pigeonholing all tank items into specific de-buff items would only favour support tanks and maybe Singed. Bruisers, Off-Tanks (think Sej/Amumu/Zac) and Juggernauts would all suffer if a change like this goes through.
Tanks should be there to absorb damage for their team allowing their carries to do what they have to.
This is a very limited view of what a tank is and it seems to assume that all tanks and based on your comments even tanky champs are support tanks. Most tanks aren't support tanks.
The best way to think of how tanks are balanced is to imagine a triangle, at the corners of that triangle put the words "Durability", "Damage" and "CC". Bear in mind these traits are relative to other tanks, so when I say something like Sejuani has low durability it means that compared to other tanks her durability is low, not compared to someone like Yi.
Most tanks have strengths in two areas of this triangle whilst lacking in another. This can be divided down the class lines of the 3 main types of tanks I mentioned before. Support tanks are tanky with strong CC but lack damage, Off Tanks are high in damage with good CC but have less durability than other tanks, Juggernauts are tanky with high damage but lack CC, since CC is the defining feature of tanks this also makes Juggernauts not tanks, although they still fit on this triangle well.
Then there's also a few fringe cases like Maokai whos only real exceptional trait is CC, but he also brings above average damage and durability without excelling at either and Singed who's strong in all three traits but has other clear weaknesses mostly in his complete lack of any mobility or reach.
These clear differences between tanky champs are why tank items need to be more diverse, but also why just adding damage debuffs to tank items really won't be positive.