Do you check the doe for readiness before you put her in the buck's cage?
The "induced ovulator" thing only goes so far; rabbit does are more fertile and receptive in a cyclic manner. Before putting the doe in with the buck, you should flip her over, and press just in front of her vulva to expose a little of the tissue inside. What you want to see is bright red, and a little swollen looking - that is a doe at her hormonal peak; a doe like that usually breeds willingly and produces a nice sized litter. If the color is pale pink, you are wasting your time, even if you do a forced breeding (people have done studies and found that the conception rate for forced breedings is generally pretty low, so most breeders don't even bother). If the color is sort of purplish, the doe has gone past her peak, and her ripe eggs are aging; though she may breed, the number of kits in the litter may be low. I have had some does that never show a darker color than a deep rose and still bred and produced well, so to some degree, you have to know your doe.
Since you are having this problem with all of your does, including some experienced ones, I have to wonder whether this may be a management problem. How much are you feeding these girls? Fat produces its own hormones; a doe that is too fat may not be experiencing the peaks and valleys that inspire breeding behavior. Netherland Dwarf breeders know this problem too well - breed a doe a couple of times, give her a break because of weather or whatever, she gains a little weight, and you may never get her to breed again! The usual rule of thumb is about one ounce of pellets per pound of normal body weight per day; some rabbits may not even need that much. Keeping a doe trim and fit is very important - so many does have died because of the metabolic mess of being overweight, some of the nicknames for the condition is "young doe's disease" and "fatty liver disease."
And of course, since these are rabbits with breeding experience, I have to wonder about Rabbit Syphilis. Are there any scabby/pimply looking areas on these animals genitals? That will put a rabbit right off - a buck with vent disease (Treponemotosis) often won't even mount a doe. While highly contagious, it is also treatable with antibiotics. A word of caution - do not use antibiotics "just in case" with rabbits; rabbits are dependent on the beneficial bacteria in their digestive systems, and they can be killed off very easily.
