For great many businesses way past the "hobby" stage, a managed DB + managed queue + managed cache + a few VMs under managed k8s + serverless functions is plenty enough. Given a right architecture, this could serve a million paying customers. When you have more, you usually have the resources to consider a more elaborate setup.

I'd say that for most businesses 3-4 VMs, or a couple of bare metal boxes, is already enough, unless they grow explosively.