User blog comment:AcesRockz/Bloodlust Decline/@comment-24474109-20160225171734

Iirc the main reason it was nerfed where champs with in-built crit (most notably yasuo and tryndamere) because those could abuse that keystone mastery very early in the game. and after the nerfs to it (so it only triggered on champs) p much everyone started favoring thunderlords because it was the only one to be buffed in 6.1 iirc.

And even then, it was the only keystone mastery that doesn't give you any innate damage. every other keystone mastery can technically be triggered in the first minute of the game, warlord's bloodlust however doesn't give you anything unless you have crit chance, and it only becomes effective after you finished 2 items. so for 2 items you technically don't have a keystone mastery.

the new version of it is much better and much more reliable, although it now fits a different class of champions which are fighters that thrive off of low health. so the change did make it more viable but its niche shifted