Larger massive multiplayer capability was one of the features Google was touting upon Stadia's launch:
Over time, Buser [Google’s director of games] says we should not only see additional exclusive games on Stadia, but also cross-platform games doing things on Stadia “that would be impossible to do on a console or PC.” Instead of dividing up virtual worlds into tiny "shards" where only 100 or 150 players can occupy the same space at a time because of the limitations of individual servers, he says Google’s internal network can support living, breathing virtual worlds filled with thousands of simultaneous players. https://www.theverge.com/2019/6/6/18654632/google-stadia-price-release-date-games-bethesda-ea-doom-ubisoft-e3-2019
Because everything ran locally at a datacenter, the real killer app of Stadia would have been a super-massively multiplayer game. There wouldn't be any problems with latency between game states, (any lag would be between the server and the console.) Imagine massive wars or mediaeval battles with thousands of participants. They never developed games that took advantage of what was unique about the platform.