The PCT has fewer people attempting thru-hikes, but they start in a more compressed time-frame and they have a higher completion rate. Only two people I knew dropped out after CA, and one of them wasn't thru-hiking.
And for those few who did quit, they missed some of the most spectacular parts of the trail. While the Sierra is a remarkable area, there are plenty of "big rewards" (as you call them) farther north -- the Three Sisters Wilderness, Crater Lake, Mount Jefferson, Mt. Hood, the AYCE breakfast buffet on the side of Mt. Hood, Goat Rocks Wilderness, and Glacier Peak -- and that's just off the top of my head.