Lack of money.
Also 2000 was a business OS
That was the thinking of a LOT of folks - 2000 = NT 5 = business/corporate OS. However, what got me curious was that - even in NT 5 clothing (remember, the OS through the first two betas was called NT 5 Workstation and NT 5 Server) it included DirectX - a decidedly non-NT thing to do. Why would Microsoft include a gaming-targeted (for the most part) subsystem in their business OS unless it had plans on leveraging that business OS for gaming? Turns out that Microsoft was dead-on - as long as you didn't use a 16-bit installer, your Windows-based games could indeed run on the still-beta Windows 2000 Professional. (At this point, while I had heard about Neptune, I hadn't seen it yet.) I already knew that Microsoft did NOT have plans for another hybrid 9x-style OS, as they had stated - publicly - that 98SE was going to be their last such OS - in a joint press conference by Jim Alchin (then head of Business Operating Systems AKA the NT Group) and Alexander St. John (then Microsoft chief evangelist for DirectX). I had been a beta-tester of 98SE - the joint presser by Alchin and Alex St. John set off the alarums. The fact that it had better performance AND stability than 98SE - let alone ME - on the same hardware (and running the same software) sealed the deal - 98SE would be fired, and replaced by 2000 Professional.