I read several articles regarding the Magnus Carlsen Invitational 2020, where Magnus Carlsen invited 7 of the world's best players to compete with him in the first professional online chess tournament. However, I couldn't find an explanation of why Magnus selected these particular players.
My initial thought was that he would more-or-less invite players from the 2020 Candidates Tournment. However, this turned out not to be true since, for instance, Wang Hao and Alexander Grischuk, who qualified for the Candidates Tournament, did not participate in the Magnus Carlsen Invitational. Alireza Firouzja, who was invited to the Magnus Carlsen Invitational, did not play in the Candidates Tournament.
My second thought was that Magnus would choose the top-rated players. However, this doesn't seem to be the case, since, in April 2020, Alexander Grischuk, who was not invited, was #6 while Anish Giri, who was invited, was #10.
My final thought was that perhaps Carlsen just invited his friends. However, this doesn't seem to be the case since, e.g., there seems to have been some friction between Carlsen and Giri.
So, on what basis did Carlsen invite players to this tournament?