Can they wear out? Sure they can. Fish, like every other animal, only have a certain number of eggs that they produce in a lifetime. So if you over breed or continually breed over a shorter amount of time, the timeline for available eggs gets shorter. Keep in mind, you are now dealing with modified fish so they don't necessarily have the genetic fortitude of their wild ancestors. Also, by removing the eggs from the parents, you are also disrupting the "natural" breeding cycles of the fish. In nature, if the pair loses the spawn, they breed again as soon as possible. Otherwise, they spawn more infrequently. In a tank, we MAKE them lose the spawn so they breed sooner than later. All this has to have an effect on the fish.
What many pro breeders do is to use a generation for a season or 2 then sell them off because they have the next generation in the waiting room waiting to take over. This way, they are always using stronger stock for breeding. What we as hobbyists do is keep our breeders as long as possible which doesn't always mean we are going to have good spawns for ever. In the case of Angels, their best productive years are only about the first 2 or 3 yet they can spawn, really BIG spawns even, 5,6, 7 years later. But this may mean they only breed once or twice a year as well. That's putting a lot of eggs in one basket, so to speak.
To a breeder, this is unacceptable as they need continual supply.
So, can I say for sure your fish are spawned out? No. Do they have a disease or condition that's treatable? I have no idea. But you do.
Are these older fish? Have they spawned a lot for you? Have you spawned them for a few years? If you answered "Yes" to all these questions, it may be time to retire the fish and move on to the offspring.
Hope this helps