why ResourceExhausted is mapped to HTTP status 503?

[wintermute0]

The mapping is here:

https://github.com/gdong42/grpc-mate/blob/3e265f4c5ac3b5a41e0de3cb8cfddd7a28bcec07/errors/errors.go#L135C15-L135C39

According to gRPC standard the mapping should be 429: https://github.com/googleapis/googleapis/blob/master/google/rpc/code.proto

I'm wondering is there any special reason behind this? Thank you.