But who will determine when more computers are needed to figure out what's available to give to more customers because there's been a spike in demand?

Computers don't fix everything. They just allow you to f*ck up bigger, harder, and faster, usually in the most banal way imaginable.

well can't create an instance without having quota available

and low quota is low, like 10 cpu, so start a 2 node k8s cluster with 8cpu each? nope, go request quota increase

If you want 1 instance, you're right. If you want 10 - 20 instances of one type in a region, the other poster's experience matches my own: you have to open a support request to ask for a quota increase, and that is not an automated process.

Accounts have instance count quotas; you can get them raised, but it is a support ticket to do so.

And sometimes, that is hard. I've had Azure support not able to understand what quota they need to raise / what quota is being requested. I had to at least link them to their own documentation on it… (partly the confusion is that quota support tickets allow selecting the quota as a piece of metadata on the ticket, but only for some quotas, and of course, mine was for one of the ones not listed. Why they don't just list all of them is anyone's guess.)

Nope, I went through this process exchanging more than 30 emails trying to get the instances I wanted.

"an instance" lol