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.
I'd rather wait a month or two instead of waiting for years for ROI. At no point have 1080ti's been anywhere close to being the most cost effective mining card, even with limited options, even considering electricity cost, it just doesn't work out.