It's been continuously surprising to me how much hatred some C and C++ devs have for Rust. While Rust isn't perfect, and plenty of criticisms aimed at the language are well-reasoned, the borrow checker is IMO the logical next step forward in "zero-cost abstraction" which is one of the strongest core philosophies behind C and C++.
The R4L effort seems to be structured sensibly, starting out with only allowing Rust code in (new) drivers. From what I can tell there's comparatively little that has to be maintained upstream, but even that is encountering aggressive pushback.
I can't help but feel like some devs have spent so much of their professional careers learning how to avoid the many footguns of C(++) that they fundamentally resent Rust for being a language which avoids most these problems, allowing fast code to be written with fewer bugs in less time and with less effort. This feeling is based on having written lots of C++ code for over 20 years, and having personally encountered devs who deeply resent Rust just because it's not C.