Honestly, I'm not even sure that they have a fiduciary duty to recover peoples' BCH. They have custody of BTC; can they really be expected to monitor for every possible fork of the network that breaks BTC's consensus rules and pay customers on that fork? I don't think so. I think that exchanges mainly supported Bitcoin Cash because their customers pushed for it, so they could dump their BCH on Bitmain.
The fork was really rushed, and Gemini is one of the most conservative exchanges, being a regulated US exchange. It's not surprising that they took this long. They need to worry first and foremost about keeping their BTC held in custody secure. Then they need to build a secure system for dealing with BCH. Coinbase won't have BCH withdrawals ready until the end of the year or early next year.