You're talking about what should be the case, not what is the case. In the real world, just as there are plenty of services with poor password practices (e.g.

You're talking about what should be the case, not what is the case. In the real world, just as there are plenty of services with poor password practices (e.g. restricting people to numeric PINs when longer-length alphanumeric passwords would be much better) there are also services that don't offer multiple user profiles tied to the same account. It's fine to point out that these services should implement such a feature, but OP's question is about what to do if you need shared access to a service that hasn't yet implemented such a feature.