That is not the technical side here.
The principles speak of hardcore gaming/gamers, casual gaming/gamers etc, proclaiming to focus on hardcore gaming with various points (sense of achievement, enduring the consequences of mistakes either...)
But every player comes with different availabilities, committment opportunities etc
Even when relying only on players who want to play games that fit the depiction set out in the principles, synchronisation of each relatively to their availability, committment must happen.
Two players playing 400 hours per year this game might not allocate their time the same way.
One might play 20 hours per week over 20 weeks spread unevenly while the other might play 8 hours every week.
Synchronization must occur. How to make sure that those two players who want to play the same game but cant play it at the same rate can coexist in the same game without one feeling/being deficient to the other?
Committment: some players might be able to meet a fixed schedule, with meeting points while others might only be able to play when they have a window to play.
Same hours played over the week but with a different level of committment.
Synchronization must occur.
All these players want to play the same game designed on the same principles.
It is indeed part of the design to answer the synchronization issue.
And the conclusion given by others migh be the right one: players ending with having one thing only in common: having nothing in common.
Following the only possible answer is the surrender of synchronization, designing the game so that there is no requirement to synchronize. Hence the solo play.
Players can play without bothering about synchronizing with others when they play solo.