this is more an attempt at an explanation, because I think there is no conscious system behind it. There are simply two ways to get to a new game - via the Matching Tab with the Automatch function or via the Tables Tab and the Join function.
I assume that the great majority of users use the autoplay function, but in the end there is also the tables tab, which always shows the newly created tables first by default - this is due to the alphabetical order of the possible statuses (new, post-game, running) - so the status NEW is always at the top of the list. And I think it's the easiest thing for some players to just press the join button for the top new table in the list - that's all.
As you may know, I'm a fan of multiplayer games and sometimes I also look at the tables list for the newly created or running 3-player games. If I know the host of one of these tables, I have pressed the join button several times to get more or less unasked directly to one of these tables.
And I think that for the 2P games it is ultimately the same intention and approach.