These protobufs are being dumped as updates come in the SteamTracking repository.
Protobufs are dumped using SteamKit's protobuf dumper.
Each folder has the google/protobuf/descriptor.proto of its binaries, which for games has options such as boxed_type that the stock one doesn't have, so compile each folder with that folder as the import path, for example protoc -I csgo csgo/usermessages.proto.
For protobufs dumped from javascript files (in webui folder), we have a separate dumper which parses javascript files into abstract syntax tree and tries to find all the messages and services. As such, these dumps are not as complete as dumps from binary files because minified javascript files lack some information.
Note
Artifact and Underlords protobufs are no longer being updated automatically.