Also fitness. The Covid "sheltered" population is also the Instagram generation, it's easier to get inspired, feel pressure from social media, or find information about how to become muscular. It's at odds with drinking.
There could be a link there. I've known people with eating disorders who only drink spirits because of the calorie content.
Ubiquitous cameras and social media surely play a role. Each and all of your drunk stupidities can and will get recorded and posted to your social group for eternal humiliation.
This I think is the key here. The traits I would associate with Millennials and Gen Z are all related to reacting to being watched all the time. And while alcohol can help a bit with anxiety, zero tolerance for just being a kid breeds a culture where doing anything that can be clipped is a bad idea. Basically, they are boring kids because anything at all that can be used against them is. I really feel sorry for them. If time machines existed and they could see how kids behaved in the past, I think they would destroy all their phones and computers immediately.