While I'm sure they take into account that people prioritize their purchases, 1st week releases have the best real estate in stores, they're in ads, and they have fan awareness so they sell better than they're probably ever going to sell. In other words, if the sales are not up to expectations...
Yeah, Sony probably abandoned one of the best selling TV series in history. Either that or they're waiting for the holidays to release Seasons Seven and Eight.
I'm sure there's always an exception to the rule but if you look at some of the best selling sets (The Sopranos, Seinfeld, The Simpsons for example), it's the first season of a series that is the biggest seller. I guess people want to start at the beginning but then for whatever, they don't...