https://www.theregister.co.uk/2019/02/26/windows_10_slow_ring/

Windows Insiders chief Dona Sarkar has taken to Twitter to explain what's taking the Slow Ring version of Windows 10 so long: It's all about the gamers, apparently.

In a sequence of tweets, Sarkar admitted the problem was a bug caused by gaming anti-cheat codes. Since it wasn't hardware specific, a staged release is apparently more trouble than it's worth and the team isn't keen on releasing something likely to blow up in the user's face.