Entropy is amazing, and its a good replacement for red buff. The very concept of "Phage + BF Sword" is ridiculous, if nothing else.
Kitae's is an item that SHOULD be good, and can even be cost-effective when the enemy manages to stack somewhere above 2.2k HP, but the real reason why it falls apart is because it:
A) It is compared to Wit's End. Even though Kitae's has scenarios it can be superior to Wit's End, people look at the two items and say "Which of these do I want? Wit's End of course, this is the quintessential Tanky-DPS AS/MR Item in the game. I CANNOT go wrong buying this."
B) Quite simply, it just doesn't feel like it shreds. It's a shredding item but you don't FEEL like a cheesegrater when you buy Kitae's. Your damage goes up, but that happens when you buy other items too. The impact upon the player is unimpressive.
C) Wit's End has a distinct player-perception advantage from Summoner's Rift, it is recognized in the Meta as being infallibly viable and even was nerfed without losing any popularity whatsoever. It has a place in people's hearts and minds, and this will influence player thought. Kitae's Bloodrazor on the otherhand is "new" and has a strong association with Madred's Bloodrazor, and the negative perception of this item being incredibly cost-inefficient and a "trap" that the Almighty Theorylord Xypherous had to descend upon Valoran and strike it from the shop forever. This is not the "social-meta-perspective-environment-thingy" conductive to opening one's arms to it.
Thusly; I arrive at the conclusion that Kitae's Bloodrazor needs to be:
1) Distinguished from Wit's End, so that the player can immediately upon viewing it recognize that each fit separate niche's and should not see one as overriding the other's right to an inventory slot forever.
2) Re-designed to FEEL like a SHREDDING item. Buying this item has to make players WANT to jump ontop of health-stackers to get their visceral feedback from it, and actually get back meaningful, visible reinforcement for doing so.
3) After points 1&2 are done, it needs to be re-introduced to the community, to try to wash away the negative connotations/stigma that pervade the word "Bloodrazor" and open players up to experimentation again.
4) A task this grand likely requires the vast powers of Xypherous. To garner his attention, I suggest you set up a small candle-lit shrine outside of his office and burn offerings of papers written by PhD's. Lyte & Davin probably have a few somewhere...