With a very cold Bohemia Obscura....why would you need anything else? Lol... Man I love that beer.....
Seriously though, if your question is about you personally starting a brew pub, I know there are restrictions on foreigners owning businesses in Mexico, as well as foreigners working in Mexico or even owning property in Mexico. Obviously, these obstacles can be overcome through Mexican majority partners, trusts managed by Mexican banks, forming a Mexican corporation, obtaining permanent resident status, and probably several other options as well.
I have spent some time trying to figure out how to live and work in Cozumel once my youngest is on her own. I know just enough to know there are obstacles, so I'm sure if your question was directed towards you starting a brew pub, there are lots of more qualified people on this site that have already gone through the steps to start their businesses.
If your question was more along the lines of why no brew pubs exist in Coz, all you need for me is an never ending supply of Bohemia Obscura....perhaps a few cans of Clamato or Zing Zang Bloody Mary mix, worchestsire, and Tabasco for a bloody beer every now and then. Christian's Mojito at The Thirsty Cougar would be my second drink choice.
Good luck, I will happily drink a Bohemia Obscura at your new venture when it gets off the ground!
Safe travels,
Jay