If they are young trees they may take a couple of years off of fruiting as they grow. Some of my trees haven't put more than a couple of apples on in the 5 years I've had them, while other in the same area have fruited to the point of nearly breaking. My honey crisp fruits so heavily each year that I've had to do some serious work to keep it somewhat vertical. For the most part all of my older trees (50 years+) generally fruit heavily one year and then lightly the next.
I'm no apple expert, but I'd say that your trees are taking this year to do some rooting and vegetative growing. With luck, next year will have a bumper crop of fruits. Adding in some compost around the tree and planting some orchard companions like chives, comfrey, tansy, burdock, clover and other ground covers around the drip line of the tree can help mine minerals and nutrients for your apple trees to work with.
One other thing that may or may not apply is the concern about apple borers. If they exist in your area, it's a good idea to keep an eye out for them between May and October when they are feeding on your trees' innards. They can really do a lot of damage in a short time and rob the tree of it's fruiting ability. Thankfully either compressed air or a thin wire is all you need to kill them.
You're trees look great to me. Nice work.