Bloodthirster's "niche" got eaten up by Death's Dance
They both give 80 AD They both make you kinda tankier (but Death's dance's is stronger for the champs that would build these items) Bloodthirster gives more lifesteal (but Death's dance's vamp applying to abilities is much more powerful) Death's Dance gives 10% cdr, Bloodthirster does not. Death's Dance has one of the best, smoothest build paths in the game, Bllodthirster has one of the most awkward. Death's Dance is also 200 gold cheaper.
Even if some re-balancing took place, I don't see why both of these items think they have the right to exist. If the champion focuses on autoattacking, then BoRK is better; if the champion focuses on AD ratio abilities then they want the spellvamp and cdr. That means no room for BT.