I have 4 drives that spin down when not in use, mainly for quietness, and they've been fine for the last year. I guess the spin-up is the most stressful part of drive operation, but they're designed for it to a degree.
Your drives dying is probably just bad luck. Unless mine being fine is good luck. Too small a sample to say much.
I wish there were a way to give each drive a different setting for minutes-idle-before-powering-off, including never for the C drive.