Please explain how charging owners maintenance fees is profitable for Disney.
The management contract includes a fee to DVCMC, the management company. IIRC, this is a percentage of direct expenses. That's probably not a hugely profitable rental stream, as there are likely non-trivial indirect costs that DVCMC incurs as the management company. The real money is in selling new points.
I would think that an anticipated % of unpaid dues/abandoned contracts are built into the maintenance fee structure.
I would think so too, but I don't see a line item in the resort budgets for it. For most timeshares, it is listed under "bad debt." This is usually a bigger problem at independent resorts that are no longer in active sales, because there is no way to "recycle" non-performing ownerships. DVC (and most other branded timeshares) can and do recycle such ownerships by foreclosing, and then selling them again.
There are a couple of ways this happens. An owner might get into financial difficulty, and doesn't know how (or doesn't want) to sell it. The other big way is that the owner dies, and either there are no heirs or the heirs disclaim it. Both of these are relatively unlikely for DVC, because there is a liquid market for it---at least so far. When we get near the end of the '42 resorts, that balance might tip.
One of my resorts, on Kauai, was managed by Grand Pacific for a short while, and their strategy for recovering non-performing ownerships was to rent out the time. Unfortunately, that's a precarious situation for this particular resort, as at the time it did not have a brand name to fall back on, and it was not smack dab in one of the two big tourist areas of Princeville or Koloa/south shore. When the time came, I was in favor of moving back to a branded management company (Wyndham), becuase as part of the management agreement Wyndham would recycle non-performing deeds into their trust product and get the bad debt off the books.