The main reason roses don't bloom is they aren't getting enough direct sunlight. You say your plants are in full sun, but keep in mind they need at least 8 hours of direct sun a day. If there's a tree or building nearby, they might not be getting enough light. Also, don't go heavy on the fertilizer. Roses do like to "eat," but if you feed them too much you'll encourage them to grow only foliage. I suggest you hold off on feeding them at this point. In my garden, I prefer a slow-release fertilizer such as Osmocote that feeds the plants at a regular rate, not all at once.
Also, do not let your roses get wet from those sprinklers. Lawn sprinklers are a good way to spread fungal diseases such as Black Spot. The best way to water roses is from underneath, keeping the foliage as dry as possible. Knock Out roses aren't as prone to Black Spot as other roses, but if the foliage keeps getting wet, they can get the disease. So, here's the deal: Make sure they are getting plenty of sunlight, back off on feeding them too much, and mulch them to keep soil moisture consistent and stop the sprinklers from hitting the foliage.