Since DVC only has 50 rooms at DL, I don't think they have much leverage for a larger discount. DL is mostly a local market. They stopped selling some Southern CA AP's because they were making the parks too crowded.
You nailed it.
I've had several very lengthy conversations over the years with CMs at Member Satisfaction about the lack of ticket discounts available to DVC members. Always get the same (circular) story.
As was stated above, DVC has to negotiate any deals or perks with whatever other Disney department is responsible for them. The story I've gotten, several times so I bet it's the official "script CMs have to use on this topic, is because DVC is so small in DLR, they can't negotiate discounts like they can at WDW where a lot more DVC members visit.
OK, I said. How about maybe deciding on whether the VGC has been a success, and maybe building more DVC rooms at DLR. That would increase our presence, and according to the story line, increase DVC's ability to negotiate better (or any) ticket discounts.
I was told VGC was a test for DVC at DLR and they haven't decided whether it was successful enough to warrant more DVC rooms, or another DVC resort.
So there we have some nice circular logic. Not enough DVC members visit DLR to warrant ticket discounts, but no additional DVC rooms in the offing because Disney can't decide if VGC is a success.
Meanwhile, what you state is true about DLR in general wanting to cut down on APs anyway. Two years ago they raised the price tremendously. This year they cut back on the options of APs they sell.
When you go to DLR it's so obvious how the AP dates drive the crowds. First, pick a day when most are blacked out and the parks are great all day long. Pick the wrong day, when all APs are honored, and be ready for the crowds. Second, the crowds show up, on just about any day, late morning/early afternoon. These are locals getting to the park for a few hours, not maniacal park commandos like so many on vacation at WDW.
I had recommended they do a length of stay park discount ticket for DVC at DLR. Maybe that would even help keep more people in the parks rather than visiting other SoCal attractions. But they don't need to do anything - the crowds keep coming, seemingly no matter how high the ticket prices.
We have been lucky. While our son lives in SoCal and is a DLR AP holder, we are in AZ and are not. Luckily, we have found some great discounts associated with the (increasing) number of races at DLR. They are only good for that calendar year (I think they expire right before the Christmas season), and if you happen to be going when there's a race there (I think they also have such deals for other events, like Gay Days), you don't have to be participating (but I think you have to pick them up in person during the event) - they are good for friends as well. This is how we get our tickets. We do a lot of the races anyway, but we also get extras for a visit we like to make when there are no races. But we have the discounted tickets.