< i have eaten fruits in any shape color and state of ripeness  possible and
have yet to see those fermented fruits who are talking about.>

The fact remains that animals do seek out and get drunk on various fruits. I
remember reading of birds in suburban areas of the US falling down dead
drunk after eating rotting glossy privet fruit.

The amount of fruit required is not large: 2 normal sized apples will make 1
standard drinks' worth of cider.
turning into vinegar requires aerobic fermentation which would not occur
under the skin, likewise for mold development.  In the case of blackberries
perhaps the very high tannin content keeps them stable.

BTW, have you eaten wild crab apples?

 andrew