VST3 doesn’t support MIDI (*). This is a hack to get around that. Go bump this thread (been a problem for years) to annoy Steinberg into supporting MIDI instead of workarounds for input and output.
(*) there is a special output event that most hosts now support for plugins sourcing CC messages and this may not affect you, but it’s arguably a half measure, and there is no general support for MIDI i/o in VST3 plugins which is a problem, given that MIDI 2 is around the corner.
\rant