It's a relative to the RSS model [ETA: or email is maybe a better analogy]. Scaling happens naturally as both more instances show up (scaling out) and individual instances scale up.

Every instance's own business model is often somewhat unique.

My primary instance at this point is on a domain I registered ages ago that I point to a SaaS host that runs and keeps up to date a growing number of small instances. I'm their customer and I expect them to charge me fairly based on my instance usage (CPU, bandwidth, et al) appropriately subsidized by their scale versus if I was booting my own VMs/containers and running it elsewhere.

If the worst happens, I expect I can move my business elsewhere, and given I control my domain itself, I can (use a data backup to bootstrap a new instance somewhere else and just point my domain DNS to the new instance).

There are a variety in business models among instances and the people hosting them.