Part of her antipathy to this sort of food is hinted at when she has a child ask for junk food or sugar cereal instead of a brand name. The same woman who eats a normal hamburger and talks about how she can't find the right kind of sawdust to make the ones she makes like it owing to her not even being able to conceive of the fact that Mother made them all wrong in the first place thinks of fast food and Frooty Bonkers as horrible non-foods imposed on her by bad people who don't want her to show her children her love or express her creativity by cooking casseroles that sit in their stomachs like lead weights thereby preventing play or making cereals that go down like a bowl of wood shavings and come out like a blazing ball of hot, wet thumbtacks the very perfect breakfast.
What makes this far more annoying is that she can cook crap that's a lot damn worse than anything on tap at Golden Corral or any of those other sterile, depressing places where arteriosclerosis is king and think that she's prepared a healthy meal because her hands make greaseburgers and tuna cardiac-arrest casseroles not fatty messes. This inability to see that just because she makes stuff by hand doesn't make it healthy and good once collided with her inability to see that her elderly father simply could not eat the foods he was used to eating if he wanted to live. This is why I think that Elly straight-up murdered Chinnuts with her lovely cooking. She'll deny it forever (or until she pitches forward dead into her plate of Cheapie Weenie Casserole) but she did kill him with kindness.