Why? Because non-stick cookware and some other items are usually coated with a chemical known as polytetrafluoroethlyene (PTFE), the most popular brand of which is Teflon.
"Teflon toxicity" which is usually quickly fatal to pet birds and occurs when Teflon coated products overheat. However, other household products that are frequently coated with PTFE include air fryers, oven units, frying pans, drip pans, heat lamp covers, irons, and ironing board covers, etc. Although cookware and associated kitchen items are more often to blame as they are more likely to overheat.
Teflon toxicity acts quickly and is deadly to birds. Very, very few birds survive this deadly scourge and the best way to deal with it is to make sure that your house is free of all PTFE coated items.
My wife and I would love to own an air fryer for our kitchen, but as they all contain at least some PTFE components we have decided that we will not be buying an air fryer as we love our pet bird and value her much higher than being able to use an air fryer.
We have also made certain our bakeware like biscuit/cookie sheets, cupcake sheets, cake tins, frying pans, pans, saucepans, bread tins, cooking pots, roasting pans, egg poaching pans and other kitchen items such as non-stick coated appliances, such as ovens, grill plates, electric pans, space heaters and drip trays are all non-PTFE.
https://www.teflon.com/en/consumers/teflon-coatings-cookware-bakeware/safety/bird-safety
https://birdtricksstore.com/blogs/birdtricks-blog/non-stick-cookware-kills-another-parrot
(Image courtesy of Gabriel Vera from Pixabay)
Incidentally I'm dubious of using PTFE items even if people don't have pet birds.