...which at the same time are collecting huge amounts of data ("telemetry") on and locking down their OS against users, as well as blatantly advertising to them within that OS. The openness is just a facade to entice people away from seeing that other side. IMHO they're basically saying "we're open-sourcing our IP because it's not worth much anymore --- monetising our users is worth much more, and they might trust us more if they think we're friendly and open."
Google and Facebook are other examples of companies doing a similar thing --- they contribute to and maintain lots of open-source projects, but that's not where their profit comes from.
From that perspective, I'd rather have the old MS back. Windows was sufficiently open to develop applications for (I've been programming in Win32 since the Win95 days), a little RE ala Russinovich went a long way towards "opening" the darker parts, and Microsoft wasn't hell-bent on tracking users and turning their PCs into advertising platform that MS controls.