You could, but they don't, meaning their argument is still sound (whether they _could_ use a single host is besides the point, they're not doing that).

Are you sure they’re not?

They’re multi-region, but that doesn’t mean they’re running across multiple hosts in each region.

Docker compose doesn’t support pooling multiple hosts, so if they are running multiple hosts per region then there’s a lot more complexity to their setup than they’re documenting in that blog. Even if that complexity is human toil managing each host as a separate entity.