What I say is that we massively underestimate just how fast computers are these days
A common story is that since day one you just have lightweight app servers handling http requests doing 99% I/O. And your app servers can be deployed on a cheap box anywhere since they're just doing I/O. Maybe they're on Google Cloud Run or a small cluster of $5 VPS. You've built them so that they have zero deps on the machine they're running on.
But then one day you need to do some sort of computations.
One incremental option is to create a worker that can sit on a machine that can crunch the tasks and a pipeline to feed it. This can be seen as operationally complex compared to one machine, but it's also simple in other ways.
Another option is to do everything on one beefy server where your app servers just shell out the work on the same machine. This can be operationally simple in some ways, but not necessarily in all ways.
I used to run a webmail system with 2m accounts on hardware with less total capacity (ram, disk, CPU throughput) than my laptop...
What's more: It was a CGI (so new process for every request), and the storage backend spawned separate processes per user.
I think people have a warped perception of performance, if only because the cloud providers are serving up a shared VM on equipment I'd practically class as vintage computing. You could throw some of the same parts together from eBay and buy the whole system with less than a few months worth of the hourly on-demand cost.