The worst thing about Stadia was the squandered opportunities. Had Google actually put some effort into marketing it, it could have really succeeded. The tech behind it worked amazingly well. I played Destiny 2 on it from launch to the service's shutdown, and it was a fantastic experience. The latency was nowhere near as bad as people (who often never even tried the platform) would claim, and it was also the best place to play Cyberpunk 2077 at launch, as it was somehow the most stable version of the game. Streaming to YouTube worked very well, and some of the integrated features with YouTube (where viewers could interact with certain games) were also kinda groundbreaking.
But somehow, Google couldn't be bothered to advertise the product at all. They ran 1 Super Bowl commercial which didn't make a whole lot of sense to the average viewer, and then basically zero marketing after that. They refused to inform the public about what the product is or how it worked or what stood it apart from its competition, which led to bad-faith reviews and rumors being spread about the platform, ultimately leading to most people who knew about Stadia being wildly misinformed on it.
It's such a shame. I absolutely loved Stadia. It fit my needs perfectly. None of the other streaming platforms I've tried have even come close, even today.