Suggesting that a predator naturally craves the flesh of creatures that it couldn't possibly hunt in the wild doesn't sound very reasonable, does it? Housecats can take down big rats and possums and such, but that's about as large as their usual prey gets. Setting aside her potential (and natural) willingness to scavenge carrion like any other feline, Fluffy would have to learn to work a shotgun to get some beef. She'd have to get a diving suit and a harpoon to take down a tuna.
But we're not talking about natural prey. We're talking about the flavor of it.
Flavors can be tricky. My soy allergy gives me a pretty good sign that my ancestors didn't have any useful exposure to soybeans before my generation; I'm not genetically equipped to handle their beany proteins. But miso soup plugs into all the right spots on my tongue, and I find it delicious and entirely craveworthy, even if it does make me sick the next day.
And feline tastebuds don't work like human tastebuds. How else to explain the fact that my cats will spend hours licking each other's butts but turn up their noses at fish even slightly contaminated with tartar sauce?
So we don't really know what tuna, or beef, tastes like to your average housecat. Much as some people find that rattlesnake and frog's legs taste like chicken, cats may find that beef tastes like rats or mice.
I've met some cats who have been indifferent to tuna. But they are far outnumbered by the cats who go absolutely nuts for it.
Housecats are domesticated animals, and creatures of instinct; their ancient ancestors had to live by solitary hunting and fishing with no human assistance. In the millenia since the first wild cat crept close to a campfire to get some scraps, the world has seen a prodigious number of animal species disappear into extinction.
I wonder, then, if the ancestral wildcats who fished the shallow waters of rivers and ponds might not have favored a particular species of fish. This fish was savory, and easily caught, perhaps because it suicidally spawned in shallow freshwater like salmon. Consequently, early humans hunted it into oblivion long before a record could be made of its existence.
And while that fish is long gone, and most modern domestic cats (with the notable exception of uncommon breeds like the Turkish Angora, which is quite happy to dive right into a river after its prey) won't swim except in desperation, housecats' tongues remain tuned to appreciate the tuna that approximates its taste.