Salaries are dominant in early stage startups, and infrastructure costs becomes dominant as you scale (also probably a SaaS-centric oversimplification). You can get into trouble in the middle, where you have enough scale to be paying jaw dropping cloud bills, but you don't have the staff to move to a cheaper architecture and you may still need to focus on getting new features out to drive growth (or to attract investment).
In startups that chasm is generally filled with VC money paid to cloud vendors, but if you're bootstrapping or not looking to be a unicorn, you probably will want to drive down infrastructure costs much earlier.
I tend to agree with you, but your aside about it being Saas-centric is really important.
One need only open Microsoft Teams to see the “billing time” costs. If the billing time cost is not paid by the developers or their company, then it stop being a cost to them and it becomes an unpriced externality. Who cares, who even knows, that this app we’re writing runs slowly on regular people’s old hardware.
In startups that chasm is generally filled with VC money paid to cloud vendors, but if you're bootstrapping or not looking to be a unicorn, you probably will want to drive down infrastructure costs much earlier.