When you get options, your starting point is effectively zero because the strike price usually is zero. So if the stock goes down, you are still at zero - you just don't exercise the option. You have upside but no downside. If you have an RSU, you have the same upside and downside - 1 for 1 with the price.

Note - this isn't 100% accurate as options that are not in the money still have some value but the idea is more upside than downside.