Source?
I know a lot of people, some with children, who have enough income to drop $60 on a game every month without batting an eyelash. Busy people are often a great target market.
These people are mostly Switch players, so Stadia is a perfect upgrade for them.
Busy people are a great market if you have a product that can save them time. Stadia is not that.
Stadia is an upgrade to nothing, as in having Stadia is better than having no way to play games. But an upgrade to a dedicated games console?
Strictly console-wise Stadia is an upgrade to those last-gen consoles. But they really need to get more games on the service because that's what people are there for.
It's also more convenient to just use the screen in front of me (TV, phone, tablet, laptop) than to find my Switch and boot it up.