If you’re a developer building an app, your customers use a variety of different systems. These are fragmented and you need to support all of them, not just Active Directory.
The previous post said "the enterprise" which makes me think of a singular organisation using all of them - maybe I'm misunderstanding, but why would a single org use more than one?
"The enterprise" is jargon for "the enterprise market."
It's rare that a company will use multiple identity systems, but there exists lots of fragmentation across the large companies, which makes building a universal solution into your app very time consuming.
