This feels like the kicker:
> In the cloud, you don’t need to pay extra for a “big iron” machine because you’re already running on one. You just need a bigger slice. Cloud vendors don’t charge proportionally more for a larger slice, so your cost per unit of compute doesn’t change if you’re working on a tiny instance or a giant one.
It's obvious once you think about it: you aren't choosing between a bunch of small machines and one big machine, you may very well be choosing between a bunch of small slices of a big machine and one big slice of a big machine. The only difference would be in how your software sees it: as a complex distributed system, or as a single system (that can eg. share memory with itself instead of serializing and deserializing data over network sockets)