Well, it isn't always their choice. Bands usually put out that their touring and venues will respond with open dates. Then they try to make the available dates make some sort of sense logistically as much as possible. It's very likely that these venues were booked on Friday and Saturday.
And you don't have to tell me about during the week - it is very difficult promoting shows when my band opens for Nationals during the week. I'd love everything to be on Saturdays first, Fridays second, and Thursdays last. After that, it's all hard. But if you do it for a living (be it a band or a venue), you usually can't make a living out of working 2 days a week (especially in the underground metal area).
Anyway, most venues in the business want live shows as many days as possible to maximize profits (just like any business). Every band who tours can't play on a Friday or Saturday - there aren't enough venues.
I didn't think you were being mean. It's all good.