It's the risk of meat contamination in the scraps that is the problem (so say my hens get a disease from the meat in the spag bol, it then gets vectored away from my site by wild birds etc.
That's why there is an exception for fully vegan households to feed scraps, but to count as a fully vegan household you can't have a cat (cat food- obligate carnivore so all commercial cat food contains meat, although mine are happy omnivores tbh) and if you had a dog it would have to be fed a vegan diet and let's not go there...
That's also why you can have a non-meat cookup in your shed using separate utensils etc, and you can feed garden waste, as in trimmings, veg you've pulled out to compost etc, before it goes into the kitchen. Once it's in the kitchen it could be contaminated.
Really it's a case of a blanket ban and legislation when some people could potentially be sensible about avoiding contamination, but you only have to look at the origins of the last foot and mouth outbreak (well, not the very last smaller one that seemed to have dubious origins) to know that there's always someone who will cock it up for everyone else, with devastating consequences.
I know it sounds far-fetched but it you want a live example have a look at African Swine Fever- it's devastated pig populations across the world and could be brought into this country by someone feeding scraps with pork (from an affected country) contamination to their pigs, yes, even pet ones, which wildlife could then carry to other sites. It's a miracle we've kept it out so far tbh.