The concept of streaming games can be the future of gaming. In order to run properly, streaming games need a stable internet connection at the least.
Google is unsure whether Google Stadia can run properly on cellular internet connection. For the time being, if you plan to play games at Google Stadia, Google will require it to be connected to a Wifi network.
This requirement was confirmed by Google Hardware Chief, Rick Osterloh during the episode on The Vergecast. According to Osterloh, Stadia requires Wifi to work, at least at launch.
Google Stadia Requires Wifi Connection, but will Mobile Internet be Supported in the Future?
In the end, Google plans to launch support for mobile internet, but for now, you can only use it with Wifi.
Quoted by Ubergizmo, Monday (10/21/2019), there is a possibility that Google is also testing a service where they want to see how well they can work. Furthermore, Google might make some adjustments so that it can be more supported on the mobile internet.
Currently, Google notes that a connection of 10Mbps or greater is recommended for streaming games. Meanwhile reportedly the Android Authority, Stadia Controller will only function wirelessly on Chromecast Ultra and Pixel 2 phones or newer.
Google seems to only want people to use Stadia in the most optimal environment until they can develop more products. This prevents negative opinions about the product due to unreliable connections.