I think part of what may affect Indie Royale sales is that the juggernaut of bundles also dropped two or three tantalizing combos in the mix at about the same time. Humble Bundle #8 had several indie darlings I'd been waiting for (Hotline Miami, Dear Esther, Proteus, Tiny and Big), and just that week or the week before it was the Alan Wake series, and now they have this weekly bundle thing... so I think part of it is that they occupy a majority of the whole "indie bundle" heartshare, clearing millions in revenue each time.
I also suspect customers look at these huge wads of game, and go, "which bundle do I want?" "Which one has cuter graphics?" "Which one is has more titles?" In other words, viewing the bundles themselves as singular products, and picking only one, to the exclusion of others.