is it possible that what your cats are wanting is a lot of variety? my snick is a very picky eater -- i've mentioned that before. what i've found that really helps her eat well is to offer variety in her canned foods -- a lot of variety. i have a canned food rotation, currently 6 brands and 15 different flavors. some of those canned foods are snick's favorites, but if she ate them every day she'd soon not like them any more. so every 3-5 months i'll start looking at other brands/flavors of canned foods, and select several for snick to try. i'm pretty good at knowing what my girl would like, we've been together for 14+ years now. usually snick likes the new canned foods, though sometimes she only likes them for a short while. but that gives her more variety, which she seems to really need in order to continue wanting to eat her canned foods/continue eating well.
I have this issue with my cats . They are super picky and very fickle .. I thought I finally had two brands they liked .. I was down to one can of each and they completely refused both of them no matter how I fixed it ..
i'm also lucky that our foster, jasper, likes pretty much any canned cat food. so he'll happily finish off any that snick doesn't want (any more of).