alt Hacker NewsI don't think many orgs are using "new Outlook" to connect to on-prem Exchange because you miss a lot if you're only doing it via IMAP and "new" still doesn't support on-prem Exchange any other way. So all my clients are using classic Outlook with their on-prem Exchange servers (and really if they have EXO too because new Outlook isn't very good).
It's been gone-as-a-default for a few months now, but for a long time, "Classic Outlook" aggressively offered a one-toggle upgrade path to "New Outlook", and it got used.
Sure, "New Outlook" on Windows is still entirely broken (including stuff like, oh, re-ordering mailboxes), but on Mac it's actually quite usable, and even allows you to switch off the IMAP proxying.