What makes you think games would just be included in Stadia?
Competing streaming services here are around $10-20/month without any games included. Origin's game access is $15/month without any game playing hardware included.
So... what will stradia end up being, and at what price? Would you pay $30/month for this? When a PS4/Xbox is only $300-400 in the first place, and has a lifespan of ~5 years?
Origin isn't relevant to this conversation.
$15/month for a streaming service + $15/month for game access service equals, drum roll, $30/month.
What are you not getting here? Origin is relevant as a reference point for what the games themselves cost on a subscription.
Stadia still needs to actually pay for games, after all. Either as a subscription (reference origin's pricing), or you straight up buy them at the normal $60/pop.