Why BORK?

Sometimes champs like cait and kaisa do build it, but only if they're up against a super tanky team that's stacking health. For some champs though, it's a must have, not only for its stats and passive, but also for it's active, which can make kiting and chasing down enemies easier. Good examples of champs you should always buy botrk on are master yi, twitch, and vayne. For most champions, however, it's a situational item since it gets outclassed by outside of the situations where it's not needed.

Caitlyn has poor aspd scaling and builds crit to maximize her headshots damage instead, whereas Kaisa needs to build all 3 stats and AP adds to her passives %health damage anyway, so BoRK ends up redundant or outstatted by say, Nashors/Zhonyas