The real question is, why is it €39.99 when buying directly from Larian? Doesn't it make sense to sell with a slight discount since Larian can keep all the money vs. giving 30% to Steam/GOG?
Right now Larian/Steam is a whopping 30% more expensive than GOG.
If it's about paying EU VAT then the price should $52 in GOG for EU customers, but obviously that isn't the case here, I get $39.99 regardless of what country I pick in GOG.