I saw this exact post the other day, but I guess we're doing it again... Lemmy is too small for this quick of reposting.
This number is bogus. There's no way to quantify the amount people have spent. There's sales and also third party sellers that would heavily influence this number. Is there ever a game you buy full price and never play? I'm pretty certain the vast majority of unplayed games were on steep discounts or from a package deal of some kind.