> Most cats catch for fun rather than food I think

The hunting trigger is only loosely connected to hunger — they don't get hungry then go out to hunt, they'll often see a hunting opportunity and go for it, eating the result partially/totally/not as needed. In a situation with abundant prey this will look like they are mostly hunting for “sport”.

I assume this comes from hunt availability/success being intermittent: it is better to slightly over-hunt (and slightly overeat) to keep reserves up for a lax period that might be coming.

They say that a fed cat is a better mouser, and this might be why. A truly hungry cat will prowl less to conserve energy so have less opportunistic encounters with prey.