Keeping some context in mind is probably helpful here. The target is WASM. And if you look at the organization the repo own is a part of, it is a web wallet for

Keeping some context in mind is probably helpful here. The target is WASM. And if you look at the organization the repo own is a part of, it is a web wallet for the cryptocurrency Nano. So perhaps using a generic message serialization library is too slow for its use case since WASM's data types are just ints and floats since the parsing code can't behave like on a native CPU with things like bytes and C-structs? It would have been great if they had disclosed links to issues regarding out-of-bounds access for things like Protobuf or Flatbuffer.