Assuming the villains' canon fates play out the same, it makes sense that Steven never finds any Hidden Depths within BillCipher that he could use to turn him good. Unlike Steven's other enemies, Bill's character is two-dimensional.
Bill's nickname for Garnet, Fuse Box, isn't just a pun on her status as a fusion, but is itself a "fusion" of his nicknames for Ruby (Short Fuse) and Sapphire (Ice Box) individually.
Fridge Horror
Mr. Fryman being a member of the Society of the Blind Eye, as explained in the WMG page, would explain why Ronaldo is so erratic, sometimes to the point of being Ax-Crazy. He may have had to repeatedly erase his own son's memories whenever he discovered Gravity Falls' weirder phenomena, and since the gun has deleterious effects on its victims' mental health after repeated use...
When Steven travels back in time in "Blendin's Game", Never the Selves Shall Meet is enforced via Past!Steven vanishing, much to Greg's concern. Though it's never confirmed one way or the other that something similar happened with the twins since they live far away from Gravity Falls, imagine how much worse the Pines parents would be panicking if the past versions of the twins disappeared. Greg at least has "it's Gem/Gem-human hybrid stuff" to fall back on; the Pines parents wouldn't have that.
