I realize the thought of too far removed from wild seems like a reasonable assumption to make and you'll see this theory advanced about some species, but I don't think it generally applies to peacocks. Too many peacocks have been line bred or crossed or tank raised for generations and are still great breeders. I bred peacocks for years and among others worked with (line bred) Eureka reds for years, and I line bred mine further to get the biggest and best color. Also bred ob peacocks a little, which are hybrids and even that much further line bred for color varieties. No problems with them holding or getting fry.
I also bred ngara and benga and at least for me the ngara in particular were somewhat less productive than some of the other species I had, not bad breeders, just not as easy for me as some of the others I had. If anything, from my experience I'd speculate that the farther from wild, the less particular peacocks get and, if anything, easier to breed.
Among the things mentioned already I'd lean toward the comfort level of the females in the tank being a factor and that peacocks aren't naturally a pair breeding fish. Peacock males can be hard on females, lot of harassment, constant displaying, chasing, etc, especially a single female. Doesn't mean it can't be done as a pair, but standard practice is multiple females for a male.
A few other observations, based on experience--
Stripping eggs or stripping early can intimidate some females from holding-- not always, but it's so stressful for some individual females that they seem to compensate by swallowing the eggs to avoid the stress. Best thing ime is to leave them be for a while, let them do what they do and later on strip fry, not eggs-- actually, I got to where I always waited for fry, anyway, easier to let the female do the work. Or-- an option that sometimes worked for me for balky females was to move them to a maternity tank and let them tend and release fry without interfering at all until the female lost interest in the fry, which is what happens at a certain point. After that point she went back to the main tank.
Conditioning is a good point, but with decent food not usually something that takes special effort just to get peacocks to spawn or hold ime. With peacocks, probably more of a factor in numbers of fry than whether you get fry-- just my opinion.
Every so often you simply get an individual female that's just not a good breeder. Doesn't matter what you do, she's just not into it, so to speak. Some may not produce many eggs, some not interested in spawning, may not pick up the eggs or even eats them, or won't hold them past a day or two, etc. I'd even get one occasionally that seemed to disrupt other females from spawning. My guess is now and then you get a genetic or developmental hormone imbalance in an individual female. Same principle as in a given spawn you might get other imperfections that you'd cull out, but in this case an imperfection you can't see.
So, here's where a modified version of your thought about too far from wild could apply imo, and that is you might get a breeding line of not the best maternal females, just not passing on those traits, maybe even inadvertently being selected that way by the breeder(s). Maybe in selecting for size or color they're unintentionally selecting against the wiring for breeding-- the biggest females don't always make the best breeders ime-- then after so many generations you've developed a line that doesn't breed well. Appears as though it's because they're Fxxx, but it's not that so much as the individual fish or the individual breeding strain.
