They were still doing limited deferrals in 2016. I think they stopped in 2017 or 2018. The impression that I got was that it was a difficult program to manage for them. I think where the comparison to the majors and large races breaks down is in the demographic of RunDisney runners. In my estimation, RunDisney has a MUCH higher proportion of new runners who register for races that they've not previously experienced and don't understand the training requirements for.
Every year I see a massive number of posts in the Facebook groups that "life got away from me and I didn't/couldn't train", "I bit off more than I could chew with the training, do I have a hope of finishing with this little bit that I've done, or "I signed up for Dopey having never run a 5k because it seemed like a good idea at the time", just to name a few.
If RunDisney had an open refund or deferral policy they'd lose a sizable chunk of the field late every year. Often these realizations come too late for them to be able to fill a vacated slot with a new runner. In addition, while we're focused on the quick sellouts of the last couple of years, it wasn't that long ago that bibs were available for MW races in December. When I ran Chicago in 2018 they were offering discount codes to MW races.
I don't mean this to sound unsympathetic. I think it would be better if there were a pathway for situations like
@lookingforsunshine's. It's just that the ability to offer those worthy situations is complicated by some of the other circumstances.
The possibility of travel insurance has been raised, as well. My understanding is that there are independent companies that offer travel insurance that will cover race fees along with everything else. Maybe that's a route for folks to look into? I guarantee that if RunDisney were to offer insurance at registration, it would be a stock offering from a 3rd party with a significant mark up to cover RunDisney's "trouble" of offering it.