There are long lasting bridges made of stone, concrete and in the right climates, even wood. Not to mention rope when it suits the purpose.
Each material has its own qualities, which means its own pros and cons in a given context.
This naive belief that there will be one language to rule them all (and is name is <fill-in-the-blank> ignores history and the world outside of programming in a rather silly way.
Rust is a risk-reduction strategy. It is not a risk-elimination strategy.
There are risk-reduction strategies one can follow with C++, which offer some fraction of the reduction that Rust does (opinions vary on the value of the fraction). Rust enforces risk-reduction strategies, which in some contexts may be of value all by itself.
Language choice does not eliminate risks in software.
They don't really. It's been shown by many studies that 2/3 of security bugs are memory safety errors. That's the minimum that Rust can eliminate.
It actually should eliminate more because it also has the strong type system and tree-ownership style that help reduce the chance of logic bugs unrelated to memory safety too (similar to Haskell and other very strongly typed languages).
Unfortunately they don't break out non-memory safety vulnerabilities, but they've almost eliminated memory safety vulnerabilities by writing new code in Rust.
Nobody is saying that. But to continue your analogy, do you not think that in a world where all the bridges are made of wood it would be notable to say that a new bridge is made of steel?
Of course there are impressive projects made with C. But we generally don't build large bridges out of wood anymore do we.
Try your best to ignore the rewrite-it-in-Rust people. They're just plain wrong for that. But yes, for a niche like browser engines, Rust is pretty darn well suited.
You may as well ask "why does it matter if this bridge is made of iron".