Sandy,
I think your tree is mostly just being smart, and not taking any chances with its energy reserves. That being said, however, all of ours (mostly self-sown seedling starts that we've moved out of the flower beds) save one, are growing without issue or intervention in shade to the west or southwest. One tree that gets only a bit of southeastern shade has struggled for years. The year it did the best was when I gave it some barnyard fowl litter in late winter and a bunch of dead weed mulch in late spring. So I'd say feed and mulch it well if you decide to leave it in full sun. Deep watering (like a two-hour stint) three times a week in drought conditions should help as well.
Age to bloom is definitely a factor, too; at least it is here. If I'm remembering correctly, our redbuds are always next to last to leaf out; the only ones that are (probably) later are the pin oaks...and possibly the baby fringe trees.
