I think it exists because they've got plenty of infrastructure assets all around the world because of GCP (and are investing in more) and they're probably trying to dream up ideas to drive up utilization and gain some operating leverage on it. A consumer subscription business that depends on all your data centers would do that.
That's not a really good reason to make a product though.
I would argue that, and it allows them to reuse idle resources. Instead of everyone having to buy their own game console or pc which sits idle most of the time, google only needs to buy enough for peak demand and then they can use the idle resources for their own purposes when not in demand.
That's not a really good reason to make a product though.