How many ATPL's are there in the world? What is the percentage of the population with serious mental health issues? Having the cockpit occupied by a single pilot for hours at a time is not how you want to discover if there is
a great number of pilots are mentally disturbed and just waiting for an opportunity to kill themselves
There is also the elephant in the room and that is COVID. Pilots have been hit particularly hard with border closures and stand downs. In the US as air travel has recovered and they are wearing the brunt of over enthusiastic schedules with the result that they are having rosters disrupted and at times been left standing at the kerb waiting for non-existent transport to unmade hotel bookings. So thinking that we all just go back to 2019 as though nothing has happened and everyone is fine is naive at best and dangerous at the extreme end. So the last thing you want to do is have pilots isolated and in the dark.