Personally, unless you're going for something of Alternators level of realism; Clear plastic adds nothing to a figure. Becuase all it does is reveal the folded up robot inside; no interiors no molded details. Just "we have to shove the robot somewhere" leading clear plastic just detracting from the realism rather then adding to it, unless you tint it so dark you can't see through it at all, then why not use just regular plastic for it? Combined further with how costs are nowdays, they can't afford most the time to make clear plastic as part of regular plastic, so if they use it, the whole sprue has to be clear. Leading to things like SS Mirage's transclearent arms, or being used in places where joint friction is gonna make them break in 5-10 years, if that.