Some fruits never ripen to a state where they are pleasant to eat, no matter how long you keep them.
My theory is that this happens if the harvesting was mis-timed - there is a fine line between picking early enough for them to 'ripen at home', and picking too soon, at a stage which means they can never ripen.
I suspect that weather/temperatures before harvesting also play a part - without enough days at the right temperature, some fruits will never be edible. The widely-fluctuating temperatures that are becoming increasingly frequent probably play havoc with fruit harvesting and ripening.