Because bars are shit for socializing? No one here goes to bars alone, and the music is too loud to hear anyone talk anyway.
I've never had the experience of talking to some random new people at a bar if I went alone.
The only times I actually got to socialize with new people was joining a pub-crawl meetup.
Edit: I just checked the three breweries closest to me on Google maps... They just look like restaurant dining rooms? I don't know if people are comfortable with someone at another table talking to them in a restaurant.