It doesn't really matter who does the work, if you were writing a new DAW, you'd probably do it. But if you were working on an established & popular DAW, plugin

It doesn't really matter who does the work, if you were writing a new DAW, you'd probably do it. But if you were working on an established & popular DAW, plugin developers could be convinced to do it if there was benefit to them (more optimizations, more features, more convenience, less bugs, etc). I don't think it is currently popular for plugin developers to implement against VST themselves, the libraries you mention seem to be gaining a lot of traction, at least from my experience from trying to catalog open-source plugins on github.