Dropping Linux support is a perfectly sensible thing to suggest. When it comes to computer gaming, all of the tooling, ecosystem, and cash is on Windows.
Even in light of the work of Steam/Valve on Proton and general Linux support. The fact that Google's gaming platform is entirely linux, and a lot of other toolchains for gaming platforms are linux based?
That's a pretty short sighted point of view.
Not really, especially when there are dozens of alternatives to vivox. But it is definitely the only thing they could suggest without saying "yeah, you should use Mumble, is objectively better".