Because instead of just growing your beard out for a couple of days and trim it to be like Will Rikers, you plaster on some fake sideburns and hope nobody notices. Perfect strategy, I don't know how that would ever not work perfectly.
Actschually yes. Gene Roddenberry said that people in the future don't care about baldness the way we do. They have the option, it's probably just so inconsequential that people rarely do it.