I guess that's because having a big catalog helps your daily streams a lot and Ava only has one album with a bunch of singles, and Rosalia's one and a half album won't move much streams and only a handful of her subsequent collabs have been real hits on spotify (they all have better numbers on YT). Regarding her recent collabs the one with BB has lost steam but it's still doing amazing (and more than half of her streams are coming from it) and the one with billie tanked to oblivion. Megan has released four projects and a lot of collabs tho, so I'd expect her do better.
BTW Rosalia did 4,49M
Megan did 5.59
Ava did 5,1