So glad to hear that you're on for an appetizer and dessert!
I agree with the theory that they don't appreciate the good cooking you do.
When my IL's first came up here to visit, at different points in the trip they brought cool whip and boxed wine into our home - I knew I wouldn't have the issues my Mom had with my Granny about never being able to cook well enough (Mom must still be traumatized since she always tries to have THE impressive dish of any occasion). Nor the problem of my SIL who has the same issue with my Mom
Anyhoo I didn't realize that cooking from scratch would be a problem for them, but I think it is. And this puzzles me since DH likes to cook from scratch. Before I met him I had no idea how easy it was to make fresh salsa.
I had some tears at our last visit with them. They left to go shopping and I started the sauce for dinner (meatballs in sauce and lasagne). I made a huge pot of sauce, roasted the garlic, fresh herbs and everything. After they got home I see MIL putting meatballs in the sauce I made - I do not eat beef - and she used jarred, full of HFCS, sauce for the lasagne.