Flash gaming was hugely successful largely because the authoring tools were excellent and truly accessible. WebGPU on the other hand is like one or two orders or magnitude less accessible (as it currently stands) than typical modern game dev, which is itself nothing compared to what Flash was back in the day. So on the one hand you have a tiny number of diehard tech nerds who can deliver some labor of love, and on the other hand you have gaming companies/studios, for whom the business case of shipping games constrained to low tens of MBs is largely nonexistent.