The problem is they think narrowly with that... even if they complete the final arc, the DVDs and paraphernalia will still sell, and they have sooo much material to re-run that people would enjoy (especially instead of the flashback hell they used to do, fingers crossed that crap is done with). I mean I've watched several of my favorite series countless times and it's even more special if I see it randomly pop up on TV.
I'm far more likely to purchase DVDs of primarily canon seasons rather than primarily filler hell (or what I feel like is filler hell), also.