You just picked the "bad ones". Most of them have at least 3 recipes per appliance. Some of these constructed appliances have some of the more profitable recipes in the game. The Big Apple Oven has Liberty Cookies, Candy Oven has Candy Cookies and Candy Corn Muffins, Bread Oven has L'amour Special, Deep Fryer has Glazed Donut, etc. And each of those have 3 recipes per appliance, with the Deep Fryer having 7. So enough variety there, along with nice profit potential. Even besides those, making Easy Ovens is great just to cut down on all of the tapping you have to do when preparing food.
Check out the sticky Bakery Story game guide and click on the Appliance Parts List chart there to go to Sehana's page where you can click on each appliance to view the recipes and parts needed for them.