I know several people who started drinking less and used pot more back when they were able to get their medical marijuana card. Now that it's legal here, I expect more people have done the same.

Not everyone is a hardcore binge drinker or an all-day-every-day pothead. There are lots of occasional-to-moderate users of both, and legalization of weed has increased availability for the casual user. There are many casual users nowadays who have never interacted with the illegal side of things, and never had a relationship with a dealer.

Weed is not a direct replacement for alcohol, but it can be a preferred alternative sometimes, for some people, and legalization has made that more attractive.