Typical Google half-assery. If they wanted Stadia to succeed, they should have been investing in game studios years before so at launch they would some games to demonstrate the concept of cloud gaming and actually drive sales. After all, it's really all about the games. And third-parties are never going to do it.
But there was no plan. They just did it and hoped success would just happen.
Yeah, I feel like they should have looked how Microsoft more or less lucked out with Bungie producing a killer app for them. [1] Successfully creating a game service requires content, content, and more content.
That said, there's still space for Stadia's infrastructure to compete with Xbox/Azure.
Yeah luck was involved, but Microsoft was at least smart enough to buy a company with a good looking game which had been in development for a while. This brought down the timeline. Bungie had showed off halo at MacWorld and was initially targeted at Mac (with an expected port to PC).
Google could do this, or pay even bigger $ for a timed exclusive from a AAA publisher. Instead google started their own studios, which would likely pay off in the long run, but google doesn't have the attention span to operate like that.
Microsoft has also acquired every good mid-sized game company with a track record in the last 5 years to their Xbox Studios. They are really good at this while Google, obviously has no clue what they're doing.
But there was no plan. They just did it and hoped success would just happen.