When the SEZ was built, they wanted to do something to make it more attractive to fans since endzone seats are normally considered to be among the worst seats in a stadium. So they added backs to these seats, cup holders, and the opportunity to purchase beer.
I think that's why alcohol has always been limited to this section (and the suites).
This has been the party line, but i've always been dubious of it.
Yeah, its a perk, but I'd guess very few are doing it just for the privilege of buying a beer at an inflated price. Most are purchasing it because of the other amenities- climate controlled areas, easier access to restrooms and concessions, etc, You'll see a lot of families and kids in these club areas (obviously the kids aren't drinking beers), and I think the climate control option in particular makes it an easier sell for some of these families who may not want to be in the heat and\or cold for 4 hours.