Welcome, Grandchild4u!
They both look reasonably healthy, are they the same age? Your soil looks fairly rocky, I suppose the smaller one may be planted atop a boulder. The slope may have something to do with it, too, especially if the lower part is flooded in the spring.
Another possibility is that the runoff from the road in the background may be giving the bigger one more water, though the inevitable oil and road salt usually has the opposite effect.