In a way, the Linux kernel does power the "backbones of the internet".

There are a hell of a lot of non-linux OS's running on core routers, but yes, in a way. However BGP isn't via email.

On the other hand, I and my office mate at the time negotiated the setup of a ridiculous number of BGP sessions over email, including sending configs. That was 20 years ago.

luckily not... would be absolutely terrible to have the backbone only on linux

Interoperability and a thriving ecosystem are necessities for resiliency.

Note that resiliency and efficiency are often working against each other.