No modern platform is built like this. We have redundancies and failover options with ways to update on the fly. Why can't Disney, whose budget is much much greater than ours/our client base, figure this out?
Basically because it's not a modern platform. AFAIK, DVC and the resorts themselves are still running on a 30+ year old AS400 foundation.
MDE, the DVC website and other newer components rely on APIs to trade data between various systems.
With that knowledge, it probably works better than one may expect. Some people seem to have recurring problems with DVC accounts which I cannot explain. And there are occasional outages. But if I reflect on my personal interactions with the DVC website, My Disney Experience website and app, checking in for hotel reservations, making ADRs, entering parks, redeeming Genie reservations, reserving and managing cruises, reliability is easily over 99%.
My employer runs on an older AS400 system maintained by a third party. They invested millions in developing a new platform, only to abandon the project after concluding that the project cost many times more than projections and clients didn't want to absorb the time and expense of migrating their own operations. As a 30+ year IT professional, I long ago came to terms with the fact that having one seamless, unified platform was simply an unobtainable goal.
We could argue that Disney has deep pockets and should be willing to invest in the best of all worlds but the migration headaches alone are enough to make my head spin. Millions and millions of DVC, hotel, park ticket, ADR transactions being moved to new systems...