Of the 3 software AV1 encoders, the only one that is fully dead is the Rust encoder (rav1e). If people truly wanted memory safe encoders/decoders, they would fund and develop them.
I can totally understand why people would want a memory-safe decoder, but a memory-safe encoder is niche. Finding a memory-safety bug in a decoder is a matter of finding a single unchecked integer field somewhere; finding a memory-safety bug in an encoder requires first finding some sort of logic bug in the encoder and then crafting an adversarial input that survives a number of highly lossy transformations.
Compare the number of CVEs against x264 (included decoders don't count!) and FFmpeg's H.264 decoder.
I think these conversations are directed by the parties funding the efforts. Example: "we (large company) want a fast AV2 decoder" -> they pay a specialized team to do it -> this team works in C for the most part, so it is done in C. If there were financial incentives to do it in Rust, they'd pay more for a Rust decoder.