I guess the main advantages Steinberg created VST3, but for me personal having only VST3 plugins installed for consistency. I run VEP also on the same host as Cubase. Now I need to install also VST2 on that host. But I understand this isn't a strong business case for Vienna to implement VST3.
The adaptation of VST3 is verry verry slow. If I'm correct Native Instruments isn't VST3 at all. A small amount of plugins are VST3 only. See: https://forum.reasontalk.com/viewtopic.php?t=7508745 These are probably new developed plugins, cause rewriting excisting plugins could be an intensive job.
But a plugin manager would be much much more appreciated :-)
Cheers,
Martijn