Mostly that the coffee shops are the customer of the captive portal solution and the shop runners don't know, don't care, some combination of both that the coff

Mostly that the coffee shops are the customer of the captive portal solution and the shop runners don't know, don't care, some combination of both that the coffee shop users have IPv6 right now so there is no incentive for the captive portal software or vendor to push the matter. Typically at this point "allowing IPv6" also really means "running two versions of the captive portal and intercept stack" rather than "moving from IPv4 to IPv6".