The jist of it is that Steinberg does not consider midi to be part of VST. period. According to Arne @ Steinberg, VST is an audio api, not midi.
Now it happens that audio includes instruments, which historically have received midi in order to produce sound. but with VST3 they are trying to remove midi completely from VST3. Instead VST3 has its own way of specifying things like notes and what sound to use...which has nothing to do with midi at all, though in some cases it may seem similar. but programmatically, raw midi is not passed to a VST3 plugin, rather these other VST3 abstractions are.
There are a few things that Steinberg didn't think through all the way in terms of how it would effect people practically speaking, that have been using midi messaging to accomplish certain kinds of things...such as sending key switches...or PC messages....or using CC messages as keyswitches, etc.. These uses of the raw midi protocol have been useful in the past under VST2 and other standards, but in some cases they have become problematic under VST3 if the VST3 way of programming these things didn't also capture those use cases.
In any case, originally people freaked out about no PC message, but Steinberg replied repeatedly that it can all be done with Program lists, but that plugin makers would need to modify their plugins to use those instead of looking for raw PC messages.
CC switches are also not a good idea to use with VST3 plugins. They will work, but can be problematic if you have a chord of notes on the same timestamp with different articulations per note, using CC switches instead of noteOn keyswitches... That scenario breaks down with the VST3 approach and unable to directly send raw CC messages in to the plugin. The VST3 way to handle that sort of thing is with NoteExpressions (programmatically), but about the only DAW that uses NoteExpressions is Cubase and even their own ExpressionMaps are not using NoteExpressions to handle cc articulation switches, even though they should be...which means the chord problem I mentioned can happen.
This can be a deep topic.
In any case, its basically on plugin makers to adhere to VST3 program list in order to fully support using PC messages in the track to signal articulation changes.