Answer: Since the trees didn't have blossoms, one explanation could be over-fertilizing. Heavy feeding with a high-nitrogen fertilizer can result in lots of vegetative growth at the expense of flowers and fruit.
Where are your apple trees located? Apples set fruit best in a location with south or southeast exposure, ideally, on a slight slope. The slope helps cold air drain away, eliminating "frost pockets." (In the spring, when buds are being formed, they get zapped by the frost that collects in these cold spots.)
Some apples varieties tend to bear in alternate years; you'll get a big crop one year, and very little fruit the next year. Proper annual pruning encourages a more consistent crop. Note also that some apples, especially those on standard (non-dwarfing) rootstocks can take 6 to 7 years before they bear a respectable crop.
Remember that apples are not self-fertile, so you need two or more compatible varieties to insure pollination. Some particularly good pollinators include Golden Delicious, Cortland, and Jonathan. Poor pollinators include Winesap and Gravenstein. This wouldn't account for your lack of flowers, but it is a common cause of poor fruit set.
Q&A Library Searching Tips