No fishing. If we took out 10an per year there wouldn’t be any bass left. There’s no small ones seen or caught when it is rarely fished. Only send largemouth. Nothing else. There’s no vegetation in the pond either.
Then that means one of two things. 1) There is absolutely 0 habitat in the pond where the fish can reproduce. or 2) The bass are eating every fish that is being hatched in the pond. Each bass needs to eat 10# of fish per year to add 1 pound of weight. But tehy can add that weight by eating 2# of good commercial fish food. So if you stop feeding the fish in the pond the bass will start looking for a lot more fish to eat. A Bass that is is 15"-16" should weigh around 1 3/4# to a hair over 2# (or more). Next floater that you find that isn't partially consumed, get a weight on it.
If either of those is true, then you are already headed down the slope to a LMB stunted pond.
BUT that doesn't help your bass dying situation now. With no vegetation in the pond, I have to assume you have a phytoplankton bloom? What is your water clarity? i.e. if you put a secchi disk or white coffee cup on a string, how deep is it in the pond before it disappears from sight? Let us know about your water temp.