VST3 and MIDI CC pitfall

(I am just a beginner in coding VST plugins, maybe i have overlooked anything.)

So it was never thought of designing “real” midi VST3 plugins?

I recentley did this juce beginner tutorial: hxxps://docs.juce.com/master/tutorial_code_basic_plugin.html
(cant post links, so replace xx to tt)
VST2 version works fine upon setting plugin midi in and plugin midi out in projucer. While VST3 plugin simply doesnt work.

What is the solution to get the VST3 version working?

Also Why is it so bad to not allow 3 VST3 plugin versions? MIDI FX, Audio and Mixed aka Synth Plugin?