Fat people who lose weight super fast end up looking dyel because of how fast they lost weight, not because they did cardio. If you cut on a 3000+ cal deficit, you'd lose a shitload of muscle as well. Technically, if those people were to cut on a 500 cal deficit and do it the slow and steady way (which would take forever, why they don't do it), they could actually end up revealing a nice physique that has developed over years of hauling around hundreds of pounds/the strongest bulk ever, provided loose skin doesn't ruin it.
Cardio simply increases your deficit, really. If you eat at a surplus, you can do all the cardio in the world and won't lose gains. A lot of people trying to lose weight do cardio because they're rather create a deficit that way over just eating less.
Doing cardio BEFORE lifting can make you feel like you're losing gains because the cardio depleted glycogen deposits before you ever picked up anything heavy. The whole "cardio kills gains" thing is one of the dumbest broscience myths around.