Cats don't pooh of course!
They just hide it in a neighbours garden.
That's largely because people are either too lazy to provide decent indoors toileting facilities (number of trays should equal number of cats in household +1) or are the sort of people who believe that their cat(s) should be locked out during the day while they're at work or during the night when they're asleep so as not to be bothered. Neither is considered responsible behaviour by the vast majority of cat people.
Madam Lexi comes inside to use the tray, and then trots off back outside.
Of course, you also can't legislate for ferals, strays and dumped cats, *especially* entire males, who mark the boundaries of their territory by toileting - and not burying their deposits. It's their way of saying to other cats "bugger off, this is MY patch" which is exactly how cats of all sizes behave in the wild. Oh yeah, and Eau de Tom Cat is bloody minging.
If a cat toilets in your garden, there's usually an arsey Human behind the problem.