I learned this by playing balanced hackmons, where the more you ascend in the ladder the less Spores and more Dark Voids you see. The thing is that even if Spore has 100% accuracy, it doesn't affect Grass types or pokemon holding Safety Goggles, while Dark Void can put any pokemon asleep, so that rule makes sense in a metagame where you can play any pokemon. However, taking into account the teambuilding limitations of this week, where Amazon has a free access to any grass type while other nations don't, I think banning Spore could be a reasonable idea.