* "disturbable by default" is a carry-over from landline-only time

* calls where rarer in landline-only time because they (sometimes) cost _money_

* calls where rarer in particular times (eg late at night) because of a social norm

* calls in the middle of the day where probably rarer, but also much easier to ignore because you were not at home and your phone simply run in the void

* calls were mostly done by human beings

Now, the "phone calls from a human being who respects social norms or that I simply never hear" have been replaced by "automated notifications from bots in a piece of plastic that's constantly in my pocket, or text messages from people that expects me to be reachable at any time."

So, I would argue that "disturb" was always the default mode, but the disturbance is now high enough that we might want to reconsider.

Although, the old rules like "don't call me after 11pm unless it's an emergency" would be hard to translate to "don't text me after 11pm unless it's an emergency even though it's currently our only way to communicate because lockdown" ;)