Let me start by saying that I whole heartedly support a better beer selection on board. I enjoy good beer and have brewed my own in the past. Can't say that I like Shiner bock though. Kind of bland. Pete's or Sammy, now were talkin'. Better yet, Sierra Nevada Pale Ale.
Back to the topic at hand, I think the current selection is a result of cost (lowest bidder) and wanting to avoid glass for weight, breakage, injuries, labels falling off etc. Plus, no glass allowed in the cabin during pre-dep drinks, that means one cup delivered, not the whole bottle, or can like now (and if you recall, we used to serve pre-d wine in a glass).