If there are things you cannot find, please let me know, and I'll try to point you in the right direction.
There are many legitimate reasons (to us anyway) for the switch - security, developer community, plugin availability, extensibility, support community, level of active development, user community, code base, built-in mobile support, real-world examples of successful migrations from vBulletin. And we looked at not just two, but several forum platforms, including vbulletin 5, Xenforo, Vanilla Forums, phpBB, Invision Power Boards and bbPress (by the makers of Wordpress) over the course of 18 months. I would say that's pretty extensive. You have to remember that we also had to move 10+ years worth of users, posts, threads, images, uploads and URLs to any new system, and that fact alone reduced the potential pool of platforms significantly because they couldn't handle that amount of data securely or efficiently.
No millennials here. Just our design and developer teams that have been with us close to 10 years and have worked on almost every major front-end and back-end change we've made.
We're making adjustments where we feel they are needed. Many issues brought up by other members have already been attended to or are being actively worked on, so change is happening. But overall, we are happy with the result of the switch. Many others feel the same. If you spent more time on the website, and especially the Forums, we'd think you'd experience this too. But you are quite right, what's done is done. Some of our changes may be too much for some users to embrace, and for them a decision will have to be made on whether they stay or go. We'd rather they stay, of course, to give the changes a chance. Because we've got more to come, to be released in the coming weeks and months. Thanks for your feedback.