The use of "back yard" refers to the local area, not the literal extent of one's property. This usage is not unique to NIMBY and it's derivatives. YIMBY sentiment also clearly extends beyond developers themselves and simple libertine principles. Many people want development to occur around them, in their back-yard so to speak, because they prefer it occurs. The semantic change you're arguing for erases this concept just to sidestep the notion of local community. It's a needlessly aggravating approach when the simple answer is just that both NIMBY and YIMBY advocates can support their cause beyond their own area because they believe their cohort is right and deserves it.