I'm not a physicist, but apparently if stainless steel has more than 2% nickel (for strength), it interferes with the iron's ability to be attracted to magnets?

https://www.chicagomag.com/chicago-home/july-august-2007/q-my-magnets-donat-stick-to-my-new-stainless-steel-refrigerator-what-am-i-going-to-do-with-the-stuff-that-hung-on-my-old-one

I can experimentally confirm that magnets don't work on my fridge.