Because you can still watch something that is highly recommended? You think people only discuss shows that are week to week? Plenty of people won't even watch something unless they can binge at least a season.
By comparison, the first Netflix show I remember really watching was House of Cards. Tried to have conversations with friends about it but inevitably you'd start with "oh, what episode are you on? Is that the one with the...? So you haven't seen...?".
Discussing an entire season when it's complete is definitely less fulfilling than discussing each episode. Depending on the show, of course.
I like a lot how modern series are written and done. I find it to be massive improvement over what movies and series used to be when I was young. I like the one long story aspect of it all. I just do not want to watch it in one episode a week schedule.
A typical show went like this:
last time on dragonBallZ… 12 minutes of content… next time on dragonBallZ