I can't really speak for other breweries, but for my own its a combination of staffing, location, and Family responsibilities.
This town rolls the streets up pretty early. It's a bedroom community. If you want late night, uptown Waterloo is pretty close. We have stayed open past 9 or 10 on weekends before for private ticketed events, but your average Saturday at 10pm, there is nobody out.
So then that brings me to staffing and family. We close at 5 on Mondays and Tuesdays, cause we need to grab our kids from daycare and it's not financially viable to staff it, it's just not busy enough.
On the other side, one of my pet peeves is going to Toronto and so many breweries and bars don't open until 4pm. I like to be leaving the city by 4pm haha. Good ole Indie, open for lunch.