No one probably cares, but I'll inconvenience a few million electrons and photons.
When you book room only, you're dealing with Walt Disney Parks and Resorts (WDPR). When you add dining, airfare, ground, etc you're now dealing with Walt Disney Travel Company (WDTC). They have completely separate systems. Adding the
DDP cancels your numeric WDPR itinerary and creates a new alphanumeric WDTC itinerary. One reason is **HISTORICALLY** it was unlawful to sell "packages" unless you were a
Travel Agent licensed in whatever states. And those states took a slice of the action as a regulatory fee. For Disney, booking everything under the WDTC banner resulted in unnecessary regulatory fees. In addition, there are TA commissions, and the backend WDTC systems look more like a
travel agency while WDPR's backend a proprietary house system.
What really confuses things is that Disney does "magic" and lets you call the same number and speak with the same cast member; this stuff just happens on the backend. But I can assure you that the backends of the two companies are way different and hence why "adding" DDP creates a whole new itinerary.
Now, DVC is little bit weird. DVCMC (DVC Management Company) purchases DDP from TWDC **wholesale**. So in that case, your ressy is in third information silo. In their system, they're just adding a feature to an itinerary.
Now - I FULLY AGREE the guest shouldn't have to deal with this horse hockey. But as long as WDPR, WDTC, and DVCMC are three separate profit centers each with an associate CIO and the money for
MDE/FP+ is coming from WDPR, there's nearly zero chance of those funds being used for a ground-up re-do of the backends at WDTC and DVCMC. Not to mention WDPR outsources backend IT to IBM, while WDTC uses Sabre et al, and DVCMC uses someone else.
And TWDC is hardly unique - this kind of "silo" approach with bare-minimum integration is pretty common in the enterprise because the latest management theories favor letting business units run their own show and the mothership acting like a holding company. It's partially how you attract talent; "As president of XYZ division, you'll full run of the show. No external party to impair your profit / bonus making potential."