It might depend on where you live. Could be the plant was never watered.

Minnesota. And the other 70-80% appears very healthy and has plenty of fruit...but I have no idea if it's been like that forever or just this season.

Has the weather been very hot and dry this past couple of months?

Another thought, that tree looks fairly young and seems to be producing a lot of fruit. Sometimes all this fruit production can put a strain on a young tree. Not sure, just a possibility.