You didn't say when you first planted it, but showy hydrangeas come from the nursery full of flowers, and our expectations for them are high. We expect them to continue to bloom that well without interruption. The fact is, it takes a while after planting for hydrangeas to get established and have enough extra energy to dedicate to blossoms. In the beginning, the plants put out lots of roots, grow more branches, etc. Even if it had been in its previous spot for a few years, it undoubtedly lost quite a few roots during transplanting.
Endless Summer is a bit less hardy than predicted and a bit slower to get established. Give it the best care you can, don't move it again, and be patient. Best care would include some mulch for winter protection, because sudden cold snaps and winters with little or no snow cover can cause some bud dieback.
