Well, it's USDC which is stable and probably is less of a headache to deal with than ETH/BTC. I suppose if not very many people use it, it might not be worth the engineering time to maintain it though.
Those charts aren't loading on my phone, but I presume you mean Ethereum (not ETH, which is a currency). This announcement says explicitly that the payouts will occur on Polygon, not Ethereum. Polygon currently has much lower fees than Ethereum (though the same scalability bottleneck inherently exists).