I don't get your analogy.
The vast majority of guests are only going to go to one Magic Kingdom Halloween party once a year, tops. Probably more like once every couple years.
Between the expense and people getting time off from work or their kids' school, there's a limited window for most families to book a trip to Disney World that could coincide with the party season.
Besides, the more party nights of a particular event program Disney holds per year, the more their bean counters can rationalize spending on entertainment and decorations, since per-ticket expenditures would scale down the more parties they add.