I’ve never been to Comerica Park. I have been to ballparks where there is glass and also where there is only plastic, as well as ballparks where glass bottles are available in premium seats and not available elsewhere.
I can’t think of a single Major League Baseball ballpark that still allows glass containers (either brought in or sold). Each stadium sets their own rules, and I suspect they base their decision on plastic bottles for liability reasons (broken glass in the seats) and for player safety (drunk fans throwing empty bottles).
Every ballpark I’ve been to has either been plastic bottles, or the “beerman” has to pour the beer into a cup for you (there are many brands of beer, such as Corona, that don’t come in plastic).