According to a recent rumor, the downfall of Google Stadia started when Microsoft acquired Zenimax Media and Bethesda Softworks.
The rumor sounds surprising, but that is what the report said from media outlet Kotaku. It stated that Google Stadia General Manager Phil Harrison noted this factor during a Q&A with staff. This was after Google decided to shut down its internal game studios.
The connection seems confusing, but it seems to be about not able to compete anymore. Microsoft has also established xCloud, which was a much more preferred application when it came to Cloud gameplay. It was much more stable in terms of connection. Harrison did say factors like the global pandemic and the rising costs of game development were the factors for shuttering down the internal studios.
Take this with a grain of salt for now. It does sound plausible.