Specially because it's not a drop-in replacement for C++. As Zig is for C.
So when Zig hits 1.0 these companies will probably consider Zig much more than they do today. Understandably.
Secondly, let us know when Amazon rewrites Firecracker in Zig, Android replaces Rust with Zig, or Mark Russinovich goes to some Zig conference explaining why Azure is dropping Rust for Zig,
"Mark Russinovich, Microsoft Azure CTO tells Rust Nation UK 2025 why Azure is moving to Rust from C++"
But in the video he says they are starting with critical systems first.
Emphasis on starting.
So yeah, not as pervasive as you, the evangelists or that video title implies.
"Microsoft is Getting Rusty: A Review of Successes and Challenges - Mark Russinovich"
https://www.youtube.com/watch?v=1VgptLwP588&t=1903s
The only Microsoft divisions that are still all are into C++ is Windows and XBox, and still, C++/WinRT is now in maintenace, the team has moved into windows-rs, WDK now has Rust bindings available.