Boomers drink less because they’re geriatric. 

Millenials are getting older. Many are on anti depressant/anxiety medication. Alcohol is a depresaant, and leaves people feeling unwell and tired. So they drink less. 

Gen-Z don’t drink because they can’t afford it. 

And cuz weed is better. Source: me
Weed is definitely better than alcohol, but I noticed many Gen Z that are skipping vices all together, unless its nicotine and tobacco.
I doubt it. This is some “everyone’s quitting social media” nonsense, people don’t stop addictive things they can still afford.