Is there something terribly wrong with VST3 that so many developers refuse to develop on it? I’d say about 80% of my plugins are only VST2.
Only thing I read about it was that some developers didn’t think it was worth the bother going to vst3. Something about there being few if any benefits technically and even some drawbacks to it. That was on Gearslutz and it was probably 3-4 years ago so you can look there if you want to dig up those comments.
Ableton not supporting VST3 for a long time was probably a big reason in the delay too. It was only last year that Ableton got support for it.
Also, i’m sure that plugins that relied on a MIDI CC style ‘hack’ with VST2.4 could no longer perform the same functions in VST3 as it was stripped out.
However, we’re now approaching the age of MIDI 2.0, so VST3 should very much take the reigns from now as it’s agnostic vs VST2 which was routed more in MIDI.
The main reason why developers stick with Vst2, is because it is cheaper, faster, easier and more “free of interpretation” than vst3.
A perfectly coded Vst2 plugin will still work today. The ones that used tricks, shortcuts and “it’s easier this way” are the ones you have problems with.
VST3 requires the use of frameworks and libraries (can be wrong about the details, but this is what I remember) which makes development for VST3 much more labor intensive (and thus expensive). That being said, I’ve been told that, when done right, using the right tools, coding for VST3 should be a piece of cake.
Fredo
VST2 SDK is no longer in active development or support https://www.steinberg.net/en/newsandevents/news/newsdetail/article/vst-2-coming-to-an-end-4727.html
The use of frameworks should make things easier for devs and is just indicative of a modern SDK.
Amazing that the likes of NI aren’t fully on it yet though, but it’s not all that surprising when their main container plugin (Komplete Kontrol) you can’t even resize. I think MIDI 2.0 will genuinely play a part in the increased use of VST3 however.
Yes and in 10 years from now we’ll be talking about how many Devs have not yet implemented MIDI 2.0 properly!
Humans…
Of course it all depends on what you have in your plugin collection. The reality these days is that most developers offer VST3 versions including: Acon Digital, Sonnox, SSL, Waves, Voxengo, IK Multimedia, Blue Cat, Melda Production, Klanghelm, Izotope, Softube, Nugen, Antares, Fabfilter and many others. A notable and surprising exception is Native Instruments who do not seem to want to update at all (in my opinion a backward decision).
In fact the only VST2 plugins I have left are from NI. Apart from that, as a general rule, I won’t buy a plugin if it doesn’t come as a VST3. I think that has contributed to the stability of my system over the past few years, so I’m voting with my wallet.
Interesting POV. 
For me, this is the least important factor which makes me decide for or against a plug-in. But I use other formats like AAX and AU regularly too, though, so my preferences might be different anyway.