Cheaping out on the material will do that.
Personally I invested in some good quality plastic containers with air-tight seals and started storing my muesli in that. Looks nicer in the kitchen to boot.
The same thing has hit pasta too. Ironically I recently bought some "premium" pasta from a smaller grocery store (by premium it's basically the same price as the non-trash pasta in bigger supermarkets, but better quality because it's not enshitified) and the cardboard box with that has zero issues closing like they're supposed to.
Definitely a construction and material enshitification problem.
Currently Playing: Xenoblade X Definitive Edition (Switch), Fate/stay night Remastered (Switch), Arknights (Android)