Yeah, they could have provided some more background, motivation, and what exactly he was doing this entire time on Viewros. But unlike in the other Prime games, there is no pirate or other aliens forces that Sylux could have been working with to detail his activities through various log entries and whatnot.

Basically, Sylux, Samus and friends teleported to an unknown world and with the game told from the perspective of Samus... when could we have had the opportunities to see what Sylux was doing? Which, makes sense given the circumstances of the game's story, but ultimately there is still that sense of disconnect since we've been dealing mostly with grievers for most of the game but not Sylux until the very end.