I don't understand people freaking out over this - outside of a purely political reflex - hell hath no fury like taking away nerds' Mountain Dew and Flamin' Hot Cheetos.
Nor do I understand the negative reactions to new restrictions on SNAP - candy and sugary drinks are no longer eligible.
But regardless I have it on very good authority that with the BBB some within the Republican party wanted to limit EBT to only be able to purchase healthy food. No soda, no candy, no chips, etc. A couple calls from Coke, Pepsi, etc lobbyists shot that down.
You are right, a single box of cake mix once a year is fine. But between banning processed foods, or allowing everything, the former is far closer to the "just cake once a year" scenario. Allowing unlimited spend on junk food will in most cases lead to worse outcomes.