Well...graphics do not have language barrier, and methods of packing/unpacking for Illusion is readily available, at that. Illusion games can be enjoyed by just about anyone because it's less language and more action, so more incentive for modders. You need no graphical mods for Visual Novels.
For visual novels it's not the same way. There are heaps of those stuff lying around, and only the best ones (in whatever standard I dunno) get picked up...and eventually abandoned or progress with the pace of a snail. Also, VN engines keep getting more and more advanced, but the repacking techniques do not keep pace...or are kept secret. Translating is one thing, getting the text out and replace it with translated text is another. Compared to folks who pick Illusion stuff for the action, how many take VNs for story? To English speaking community it seems like VN is even more niche than, say, Illusion games.
Although...those Chinese folks apparently can do much...I've heard of Chinese patch for Daitoshokan no Hitsujikai (a relatively new, and advanced release) while snooping around Chinese sites...