When you drill down it comes down to people who do not clean their cat's litter box and the poop dries and becomes a fecal host.
Dogs need constant care and should never be left alone more than 5 hours. Cats can shit anytime they want and they shit and pee in the sand box. The litter box should be cleaned constantly to keep humans and cats healthy.
Cats can be left for a few days if you travel out of town. If you are gone for two weeks or more you just need a human visit once a day. The human of course must keep clean water, did and litter box. Dogs need more human intervention in order to remain healthy. You have to travel with your dogs or get a dog sitter to walk them out let them play outside 3 times a day or more.
I've seen too many dog owners use kennels incorrectly and I think that's cruel. If I had a country residency I would definitely have a dog. In the city a cat is good and two cats are nice.
But
You have to clean that litter box and vacuum the little bits of litter tracked or sweep several times a day. For clean people cats are good. For dirty people cats like dogs will suffer. Dirty people are already suffering, anyway.