I calculated how much countries we could gather just with players I already know, and I could gather more than 20 countries, and I wasn't that far from 32. Yes the issue is players not wanting to join and some not even being asked because they are not known in the taiko community (ie. people think they don't exist).
About Argentina not being in pending countries, I guess it's because we couldn't gather 32 teams, so they decided to cut off the number of participant to 20, and if you sent your application after 20 teams then maybe you're not on the list. But this is just an assumption, we should wait for the official answer

EDIT : After reading the wiki page, it looks like this is the case. We now have 4 groups of 5 teams and #1-#4 of each group ascend to the knock-out stage. If we could gather more than 20 countries and having to reject some, maybe we can try to gather 24 teams, make 6 groups of 4 teams, make #1-#2 ascend + the 4 best #3. As we have to play the group stage in one single week-end, it will be easier for both part to make groups of 4 teams ?