Yeah, some people never get to feel the rush, but that doesn't matter. There is really no reason not to exercise and plenty of reasons to do so. Besides obvious health and aesthetics benefits, there are also psychological ones - sense of accomplishment, progress, self-discipline and expanding your ability to withhold gratification and endure discomfort in order to achieve long term goals, which are way more important than some endorphine high. I would say it's actually the most important of all benefits of (regular) exercise.