Things like Rust in Chromium weren’t even being talked about back when Brotli was introduced to Chromium.

I think Chromium as a project would be happier if they had less unsafe code in general, and holding new dependencies (especially those like media formats, which have a long history of security issues) to that standard doesn’t seem particularly surprising.

There’s always going to be trade-offs: how much benefit does this provide (users, developers) compared with how much risk does it incur (safe/unsafe code, quantity of code you’re now on the line for the security of).

(And that’s taking that reason to not support JPEG XL at face value, ignoring any debate about it.)