@newbrain Thanks a lot for reaching out to WCH and posting their code publicly!
One of the main 'uses' of the GPL's 'viral' clause is for improvements / additions to be backported to upstream, regardless of whether the downstream developer is interested in doing that themselves. So the main 'user' of that code is going to be developers of the upstream project, and once it gets consumed this way, it's not really needed any longer. It's not that surprising that the number of requests is low, but that doesn't necessarily mean there isn't value in getting that code back to upstream.
The 'better' model of course would be for the vendor to just participate in the upstream development process, in which case the GPL's viral clause isn't really relevant, since their patches are being directly included.
Mostly end users are not going to be too interested in building/running a vendor fork, but there might be many users of the functionality once it gets backported upstream. Like in this situation, probably not many people will consume the WCH openocd fork directly, and may even choose to avoid those chips until it's integrated, but the protocol will get integrated upstream and lots of people will use that.