Stretches of small water that get lots of human activity will have few wild brook trout and brown. Maybe a few.
If a section of surface water flow is not truly suitable for wild and native trout because of high density human activities, and/or stability of stream composition, then it would seem to be a stretch/section open for temporarily holding food-strain trout. Those trout in a stream, especially rainbows, will drift downstream if weak or necessary behavior. Wild and native trout are much less inclined to hang out at the swimming hole (although they will) than in another section.
Recreational stocking of short-life expectancy human-desired food fish - trout in Pennsylvania, catfish in Texas - is for those for whom fishing is mostly occasional and social.
Sacrificial sections of water bodies for light recreational activities by fringe fishing people would seem to help overall in keeping flyfishing a respected activity of the general population.
But Class A do need protection.