It appears to me that even in games that are entirely multiplayer-focused and build around that feature, a huge part of the player base seems to be playing solo exclusively.
By “see” I’m referring to streams, VODs, feedback from friends, discussions on the internet, etc. But then when a given game gets said multiplayer mode, I see most of those people playing it solo. A certain player base asking, requesting and sometimes demanding a multiplayer mode.
I’ve seen it many times over the course of the past 20 years, in many game communities.