The best way I've found to explain it is this: Even though a DVC membership is represented by "points," those "points" actually represent a percentage of the DVC resort that you own, just like a share of stock represents a tiny percentage of ownership in a company. Granted, your DVC ownership has an expiration date unlike most (all?) other timeshare interests, but until the day expires you're technically not just a DVC member, but an owner. Your maintenance fees cover not just gardening and pool chlorine
but taxes and utilities and any sort of expense you would expect to pay in your own home, divided up amongst all the other owners of that home resort.
Now, as I said, your points represent a teeny-tiny percentage of ownership in your home resort. If DVC were to try to increase, across the board, the amount of points it would take to stay in a DVC room or villa, then what they're essentially telling you that, as of that moment, you own LESS of a percentage than you did before.
Imagine if a friend opened up a pizzeria and you became a partner with him, and you gave him enough money to be a 10% owner in his company. Then, at the end of the year, when it came time to divvy up any profits, he gives you enough profits for a 5% owner and says "uh, yeah, you bought a 10% ownership, but I decided you now only own 5%." That legally can't happen, and DVC can't legally decide that more points are necessary across the board to stay in DVC rooms. Similar deal.
The only thing I THINK they can do, legally, is make the point values for new resorts as high as they want them to be, which would make it cost (or point) prohibitive to stay in them unless you buy points there. They've already done this to a certain degree, rooms in BLT are more points than similarly appointed rooms in OKW, for example. You're paying for the "real estate." And the point values for staying at Grand Californian at DL is much higher still. When/if they ever add a DVC wing to Grand Floridian, there's no reason why they can't insist that a studio in value season go for 200 points a week, and insist on a 250 point minimum purchase. I'm not saying they will. Just saying I believe they could.