GM bought cruise for 1 billion. Softbanks stake would value it at 11 billion. Even if GM put in some money into cruise their return on investment seems pretty good.
I think it's a lowball estimate, but for argument sake, let's say they're each worth $150k. At that price $2.25 billion will get you 15,000 robotaxis, and that's far from the only expense.
Waymo has announced a plan to deploy 20,000 vehicles in 2020, and that is what GM is up against.
You just can't have enough money in the bank if you're comitted to a scaled commercial robotaxi deployment and are planning for world domination.
in 2 years from 1B->4.5B (with GM original stake of 1B growing 2.5x during those 2 years(4.5 - 1.1 - 0.9 = 2.5)). This is why i love tech. We call it "only" here.