Another commenter mentioned it, and I agree, there is something to running a calendar server of one's own, if one is capable of doing it. I've been trying to scratch this itch for years to little success, but feel like it gets closer all the time. Things like NextCloud make it even easier still, but lack the way I want to deal with groupware (service accounts). I'm hopeful that Apple Family Sharing can solve some of this for me and my partner as we both use iCloud calendars today, but haven't set it up yet.
Over all, I agree, and wish I knew the answer, but I don't.
EDIT: lazy mostly because of the hassle of importing data from my work Google Calendar, and my Apple personal/family calendars.
It has two problems (that are both dealbreakers to me): it's not easy to make it push the complete schedule into any other calendar (if it's possible at all, I never managed to), and the apps are often not reliable (probably because they don't want to allow a centralized calendar, the MS ones are serious offenders here).
I run a calendar server[0] that is my main calendar repository. And I use vdirsyncer[1] to sync to my laptop to use khal[3]. On the Android side I sync with davx5[4].
This allows me to subscribe to webcal calendars, which outlook365 offers, and syncs them to my two main devices.
Not perfect because that means I can't edit my outlook calendar from within this system ( and a reminder why open standards and interoperability are important ), but it means that my private calendars and addressbooks are self hosted.
You are right though, that takes effort. And I want to snark at microsoft for not supporting caldav, but then I am waiting for gnome-calendar to support it as well. It doesn't seme to and that feels a bit strange to me.
[0] https://radicale.org/ [1] https://github.com/pimutils/vdirsyncer [2] https://github.com/pimutils/khal [3] https://github.com/pimutils/khal [4] https://www.davx5.com/
So I looked this up now (have not tried it myself, though).
So looks like gnome-calendar should support CalDAV calendars since some time now?
https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_reques...
However, according to this issue calendars work once added but the only GUI-way to add them right now still seems to be Evolution, after which they will show up in gnome-calendar as well (also some workarounds here):
https://gitlab.gnome.org/GNOME/gnome-contacts/-/issues/70
There's a PR for proper support here but maintainers seem MIA:
https://gitlab.gnome.org/GNOME/gnome-online-accounts/-/merge...
Had some FUBAR situations where vdirsyncer tried to fix "something" (which is necessary from time to time since davmail does only rudimentary checks of events) and got im a situation where I send confirmations for 5 year old events to a few dozend people
Both calcurse and remind support CalDAV sync (experimental in the case of calcurse). calcure does not seem to support it; just opened an issue for it.
[0]: https://caldavsynchronizer.org/
EDIT: Several mentions of Outlook on software listed under https://devguide.calconnect.org/CalDAV/introduction/, maybe there is something that works for you
Since I'm an IC and never ever schedule meetings unless I really must, this hasn't been much of a pain for me.