I'm not sure how it works. Presumably, they agreed to this setup when they signed on with Track 15. I know the other locations of There, There, Dune Bros., Dolores, etc. all take cash though. I think most places account for credit card fees in their pricing.
I used to always assume merchants preferred cash until I encountered a few that adamantly preferred cards only. So I think it's a mixed bag (albeit with cash still being the preference of most). The argument for cash is the lack of fees, the immediate cash-on-hand (vs. waiting for bank transfers, risking chargebacks, etc.), and a little more "flexibility" on reporting earnings, etc. But some small businesses I've spoken with prefer cards. It's cleaner/easier with an immediate paper trail. There's far lower risk of loss, theft, etc. faster sales (usually for larger amounts), and flexibility across platforms (i.e. ordering in person, online, etc.).