I'm not sure about Clash but there are often game mechanics that kick in to heavily multiply your rewards. Spending $X gets you Y in game value but spending $2X gets you 5Y. And then it can compound with follow up offers targeted at the player/whale which may not be generally available.

So I don't doubt your figures but there's probably a "one week whale" trajectory that's built into it to give quick gratification for something like $250,000. Still seems outrageous but they can discount digital goods differently than retailers can.