1080 ti very close on both efficiency and hash/$ on MANY algorithms with anything else even as a bare card - don't ASSUME that all mining is Ethash (ETH/ETC/ECL and such) where the 1080 is a bad choice.
It also offers higher rig density than any other option that is affordable (Titan V is NOT affordable) for which some folks are willing to pay a small premium vs "max efficiency" cards.

Can also depend on what is AVAILABLE the last 3 months - sometimes you buy what you CAN get, not wait a month or two to sneak in a buy on something you would prefer IF you get lucky.