And, wasn’t batching created in the 80s? There is no reason they can’t design a program that flags new availability and holds it for waitlists.
It's not just about complexity of programming, there's also an element of deciding who should and shouldn't get the room with no clear victor, IMO.
Imagine you're waitlisted for January 1-7. Somebody cancels January 1-5. That's not a match for your request. If everything happened in real time, those dates would be passed down the list to someone whose request it can match. If another member waitlisted January 1-2 and a third person waitlisted January 3-5, their requests would both be fulfilled. You get nothing.
Now instead imagine that at 8:00am someone cancels January 1-5 and at 8:10am a different member cancels January 6-7. The batch runs at 9am, both rooms are still available, and the combination of the two matches your request. You get the room. Batching increases the likelihood that longer stays will match, at the expense of some immediacy.
In addition to the operational shortcomings, real time matching is an incredible drain on computing resources. Every cancellation would have to bounced off of literally thousands of waitlist requests looking for a match. That simply cannot happen instantaneously, meaning there would be a lag between when a cancellation occurs and when the inventory returns to the website. That lag disrupts the FCFS nature of reservations. (If someone cancels a room at 8:05am and I'm looking for that same room at 8:06am, I should be able to see it...not have it stuck in a waitlist pending queue for minutes or hours, only to have someone else grab it later.)
It's also worth pointing out that DVC has to manually adjust reservations that hit against the waitlist. And it can take several days for that to happen. When people get a room by "stalking" the waitlist, it's entirely possible that another room has already been held, but is not yet assigned. In other words:
Feb 18: Waitlist match is made, new room is placed on administrative hold waiting for CM to cancel existing reservation and book the new room.
Feb 20: Another room is freed-up for same travel dates. Member sees room by "stalking" and books manually before DVC has opportunity to make waitlist assignment.
I'm sure there is room for improvement in DVC's IT systems. But I'm not convinced this is an area that is clearly broken. Any "fixes" would introduce new / different problems.