DoesItPlay is a network of volunteers that began their work on this initiative a few years ago, so it's natural that there are still many games that have not been cataloged yet since they depend either on the pubs providing them with games to test or them purchasing those titles themselves.
Let's take the PS5 as an example. There are
over 800 games that have received a physical release on this system, and so far they have tested around 300 of them.
Similarly, most of the 500 untested games are single-player focused. If they eventually manage to cover all of them—which is unlikely without more help from the community—the percentage will lean even more towards physical releases that have a solid disc build (e.g., offline play and no mandatory download).
Also, as a fun tidbit, EA seems to be great at delivering solid disc builds for their annual sports releases (e.g., Madden and FIFA on PS5). So even with these titles that primarily focus on the live service aspect, they still put in the effort to ensure that they have a playable game (offline modes) on the disc.
So the tl;dr here is that Ubisoft can go fuck themselves.