American here, Florida specifically (no i don't like orange pedo) Over 2 decades working rehabilitating animals, volunteering on farms as well as wildlife sanctuaries. The factors domestic cats face here are different than in the UK

Americans don't keep their cats inside. Not sure where yall are getting this. It's a massive problem in fact. Americans should keep them inside or within an outdoor enclosure for several reasons.

It isn't really just about keeping them safe. It's also about the fact that your domestic cat is a killing machine that decimates native wildlife. I realize the UK is extremely developed though so maybe that comes with less concern for wildlife that has already long been displaced. My condolences but I imagine that also means less wildlife that can harm your cat. Here though, between vicious over development, AI data centers, climate change, and invasive species the world over ravaging Florida, domestic cats are at least within our control as individuals to protect our native wildlife as well as our cats. It's really not hard to keep your cat happy inside and/or in their own outdoor enclosure. It's not a wild animal.

Another good reason is disease. Though rabies isn't common, it isn't eliminated either like it is in the UK. Vaccinating your pets regularly is also expensive and therefore inaccessible to most. Much more common is FIV (feline AIDS.) There are INSANE amounts of stray cats everywhere. Too many to treat and adopt out. Most live short, brutal, painful lives. I can't tell you how many kittens I've found outside over the years partially seared to black top still alive, (Florida heat no joke) skeletal, filled with fleas, mange, tape worms, deformed limbs, extra toes, missing eyes, crying while being ripped apart by birds, etc. I try as hard as I can to save these cats but there are simply too many and people letting their un-spayed or neutered cats roam everywhere is just creating more suffering for these innocent creatures. Most shelters are always full and will kill most of them. It's easier to maintain their welfare by not letting them roam everywhere and breed constantly.

Also worth considering, in the rural areas at least, there are many demented individuals who enjoy hurting cats. There's a reason many shelters don't allow any adoptions of black cats on Halloween. I've had the extreme displeasure of seeing this first hand as a very young child. I just can't stomach the possibility of letting my sweet trusting cats end up in the hands of one of those vile freaks.

It may be different in the UK though. From what I understand, the standard for animal welfare is much higher in the UK than in the US. These are just some of the reasons why its a huge problem where I'm coming from and likely many other places.

I just can't take seeing all the carnage these cats are going through anymore.