Streaming games is not cheap, the same way renting a house is not cheap.
The biggest shock of the Stadia reveal was its cost. Most people who supported it, was in massive denial concerning how much it costs. Steaming games is far more expensive than any other kind of gaming, because it costs more money on both end; the streaming company has to spend money every time you play, and you as a customer also spend money via data every time you play. It is the least economical option there is.
Anyone who want to stream games thinking that would save them money, is very much mistaken.
One possible reason for the misconception, is that because game streaming is an inferior gaming experience, that you assumed that it HAS to be cheaper. That just because it is a worse product that it has to be more affordable.
But that's the issue; game streaming is BOTH more expensive, AND worse for gaming. The only up side, if you can call it that, is that the game companies can pull the plug and take away your game when ever they want, and force you to buy the sequel. But that's for publishers and not consumers.