Wouldn't it be even more insane if protobuf had its own distinct string splitting/merging routines, its own flags and logging libraries, etc?

No. Not at all. String splitting is a couple of lines' code. I don't want have to think about a logging framework just to read a protobuf - it can send stuff to stderr like everything else. If Google wants protobuf to be a widely accepted standard then it shouldn't require you to opt into their ecosystem to use it.