I've been on and off TDF for years and know a lot of members.
I think in general producers want to limit sales on TDF because it cuts into full price tickets and also perpetuates the idea that a particular show shouldn't be purchased at full price. I've heard many a person say "don't buy that, wait, it's always on TDF." They also do silly things like place all the TDF tickets in the last two rows of an absolutely empty balcony.
There are many lovely people and some absolute awful ones.
I'm not a huge TKTS person, but aren't the tickets at TKTS generally more than from TDF?
For Bandstand I would think the way they are marketing themselves as an old-timey musical, which appeals to an older demographic for which matinees are a popular option.