For a console? Very important!
For stadia? Not important in the slightest.
Which is this thread actually about? Consoles need 1st party games to encourage people to buy that console. Stadia is effectively just a storefront, so it needs 1st party games just as much as Gamestop needs them.
Stadia is a Streaming platform. Billed as an answer to PlayStation and Xbox by Google. If Google wants Stadia to have any longevity, or be taken seriously by consumers, it needs first party games, there's no way around it.