Walt Disney World has a huge sponsorship deal with Nestlé, including Nestlé brands such as Nescafé, Edy's Ice Cream, Buitoni, Nestlé Toll House, and Stouffer's. Think of The Land. Think of the restaurant sponsorships at the Magic Kingdom.
But just because the coffee is a Nescafé product doesn't mean it has to be the coffee that's now served in most locations at WDW.
Nescafé has a full range of coffee products that they sell to restaurants and institutions. Disney has picked a particular coffee that they apparently feel is middle-of-the-road enough to appeal to the majority of WDW's coffee-drinking guests. Nescafé emphasizes liquid concentrate coffee over freshly brewed coffee. The concentrate provides greater consistency and ease of keeping coffee urns full.
I think Starbucks coffee is much better than what WDW serves. But what WDW serves is much better than what most limited service hotels serve at breakfast. I enjoy Starbucks. I can drink WDW's Nescafé. I can't stand Holiday Inn Express coffee, at least the last time I stayed at that chain.