also some fruit varieties are proprietary so the seeds are sterilized …
Here in S FLA we have this issue. I’ve learned that rotting mangoes STINK to high heaven and it sucks to accidentally bike through some mushed mangoes in the street. A coworker has told me about seeing rats running along the rooftops in his neighborhood to go from one fruit tree to another.
Old adverts from the 30’s-50’s show elegant housewives leaning out the kitchen window to pick very conveniently placed orange trees. The only way for that image to come true would be to build the house next to an existing tree!
There’s also the fact that many seeds just don’t sprout. I am an enthusiastic but indifferent gardener, and it’s my observation that no more than half–at best–of the seeds I plant will sprout. This is true whether I’m trying to grow vegetables like carrots or native plants like California poppies and hollyhocks. I have large pots for my vegetables and after years of planting there must be loads of old seeds in there, but volunteers are pretty rare.
The exception is milkweed, which grows like, well, you know.
Plenty of feral apples, pears and plums here. But there is cool story why.
In 18 century, here around ruled Maria Theresa of Austrian Empire. She ORDERED to plant fruit trees to an any empty adequate space, to diverse food production and fight famine.
Their successors now usually thrive on the sunny sides of the hills, by the end of the forests, just in the middle of the plain meadows and on practically any other no mans land (like inside highway fences).
People just consider them as any other wild (forest) fruit and are generally used for jams, cider, brandy or animal food. Still, 99% probably just rot away.