A lot of what fuels his decisions are very particular sense of nostalgia, hence the "Make America Great Again". Old things = good.
In this case it could also be a shifting away from US farm subsidies - since much of the reason we use corn as a sweetener in the first place is it's subsidization.
It's the same reason he's against EVs, against wind, against solar, against power-efficient lighting, against improved shower heads and toilets:
To claim power. To reject the world and assert oneself. To deny change. To soak attention with negative energy, to hide from the actual things a president should or could be doing that would be at all worthy of their time. To keep people mad and riled up, following after what Ivanka reported in 1990, that he kept Hitler speeches by his bed, admired him (his ability to rile people up & thus be manipulable). The praxis of the dark side is to be ongoingly aggresive, to always bring out the worst in people. This is just another swing at that.
In this case it could also be a shifting away from US farm subsidies - since much of the reason we use corn as a sweetener in the first place is it's subsidization.