Colocation isn’t a binary on-or-off thing. As a crappy example, Kubernetes pods maintain the invariant that all containers within a pod exist on the same Kubernetes node. So you can avoid the most egregious waste of resources/time that comes from having no collocation.

To your point, when talking to your db or [insert shared infra here], then you may want to thinking about real collocation. But it very much depends on your application’s needs - and remember that cloud providers can offer guarantees about which AZ or region you’re in.