Comment by dralley

Allowing C++ would lead to endless debate over exactly which subset of C++ is allowed in the kernel, and would be a pain in the ass to police.

The point of Rust is that it offers enough facilities to the programmer that you can right near-bulletproof APIs from a memory and thread safety perspective, it has momentum with a younger and enthusiastic group of developers, and it doesn't have the problem about what to allow and what not to allow to nearly the same extent. That means the potential exists for a net-reduction in time spent reviewing code for misuses of various APIs.