Does anyone know why there's no desire to see a working standard (protocol) for calendar/tasks?

It's clear that CalDAV doesn't function consistently across devices (and does seem to be dying as a standard). If you work across different devices/OS it's virtually impossible to get things set up seamlessly. Companies and developers of task apps seem happy to create silos and not look at interoperability.

If you want to self-host, it's too hard to do this and you really are limited to a tiny number of options.