Additional timeline info, as I was curious myself. WebP is old enough that a memory safe language was not a feasible option when the project started. Android 12 was the first version to support Rust code, and came out in 2021 [0, link talks about the first year of integration]. On the iOS side (which also was affected by this), Swift 1.0 came out in ~2014. As far as I can tell, Chrome doesn't yet support a memory saf…
Is Rust in practice a memory safe language when you're doing tricks like decoding huffman-decoding huffman tables into buffers? It seems like once you optimize for performance this much, you're liable to turn off bounds checking here or there.
That said, not switching over to a memory safe language, in my opinion, is letting perfect be the enemy of the good. Folks will still be able to write footguns, but better language choices will prevent bugs in the all the non-crazy optimized parts.