Corn subsidies are another market distortion that keep sugar more expensive than HFCS.
Especially subsidies to US "Grade C" Corn serve to keep a lot of corn derivatives incredibly cheap (HFCS, corn ethanol, fatty cattle feed stock filler, etc), because "Grade C" (aka "US Standard Corn") isn't typically considered useful for much more than its derivatives but there is a massive trade in it because of how cheap that corn is.
Especially subsidies to US "Grade C" Corn serve to keep a lot of corn derivatives incredibly cheap (HFCS, corn ethanol, fatty cattle feed stock filler, etc), because "Grade C" (aka "US Standard Corn") isn't typically considered useful for much more than its derivatives but there is a massive trade in it because of how cheap that corn is.