Well, originally I didn't like 2017, maybe the UI was a shock to me, something about viewport felt odd (smoothness, glitches..). But that was solved of course, and I would get used to new UI anyway but..
..then it became fear of upgrade. I was always the guy who updated everything at once and suddenly I am four years behind :- ).
It's because 2016 is so damn stable for us, we almost never get any crashes whatsover, and even those few we did, it was Corona related. And everyone else keep always complaining about this and that in 2017/18/19/20..
But it's time I upgrade anyway because from 2020 you can't downsave to 2016 and that will become issue when working with someone who is on 2020. And also plugin support,etc..