And sometimes (which is I think what most applies to Microsoft) too many authorities that must be pleased and nobody with imperial power to say "In the interests of simplifying, we're going to piss off key stakeholders for a period of time." Microsoft's OS team has, at points in the past, rebuilt data structures from C++ to C with very specific memory footprints rather than break, for example, Photoshop (which was getting more performance from running its own OS structure allocator instead of calling the APIs designed to allocate structures).

Simple ecosystems and simple software usually have the same thing in common: they are either young, or they've recently survived an extinction-level-event. Older systems with many dynamic constraints breed complex webs.