Pet food is predominantly made from the off-cuts and waste products of the industries producing animal products for human consumption. Even pet food made from premium meat depends on the economies of scale of those industries. There no industries intentionally producing mice at mass market scale ergo there is no widely available mouse meat cat food.
People would think it was made of mice and wouldn't buy it. Even though, like most cat food, it would mostly be made out of Meat Man, the Man Who Regenerates Infinite Meat
There was an interview with a food scientist at a pet food company where this question was asked. Their reply suggested that they had experimented with mouse-flavour cat food in their testing lab, but discovered that cats don’t actually like the taste of mice compared to the meat of larger beasts humans get for them.
I don't know the answer, but I've always thought it funny that we give them things like tuna and beef. Two animals that a cat would never either encounter or be able to take down in the wild. They're eating meats they'd never get to taste otherwise.
Speak for yourself. I've been cross-breeding domestic cats with wild ones and breeding those hybrids with even bigger wild cats to produce increasingly large and vigorous hybrid super-cats. They're now bigger than mountain lions and with my training regimen they'll be able to take down a bluefin within weeks.
Maybe that's why they like them so much, it's a rarity?
There's clearly something about fish that's really attractive for cats. Maybe it's the same thing that attracts humans (my guess is the smell is indicative of certain nutrients, but I'm just throwing crap at the wall).
Though big cats do swim, so maybe there's something in the genes from their big cat forbears?
I am not a mouseologist, but i would imagine that it's due to how difficult it is to get that meat divided by how much usable meat per mouse you actually get out of the process. There's a cooking term for this involving percentages but I'm pretty high and I cannot recall it for the life of me.
Bones and organ meat are good for cats though, and they can digest fur. Plus it's done for other animals- reptilinks for example makes rodent sausages for reptiles. So it's doable. I suspect it's more to do with cat preference