I guess the right answer is that
back in old times Ayu was on top & every single was MAXI
that means it included not 2-4 tracks but more & some remixes
besides, Ayu's avex decided not to do any more remixes cuz the lastremix albums sold out badly, as they haven't expected
the other thing is that Ayu's music now is light rock & not pop
so it's hard to make any remixes of that stuff
still, nowadays, Ayu fans realli miss old good remixes