For some cats the concept of eating raw food is completely crazy because its ingrained in them to eat processed foods that require no or minimal chewing, if your cats arent interested it will take time to get them into the idea
Start small and work up, its like moving children to solids, you dont present them with a large mutton leg!
Most of mine took to it very quickly but tabitha and milly have taken more work but now they can both chew cubes of meat
im hoping milly will get to it as shes going to need another dental this year which will be the 2nd since iv had her