Without going into too much detail, this "coupled account" problem is taken very seriously internally (AWS Identity dev, my opinions are my own and I don't speak for the company).
There is a very large project to fix this. But as you can probably imagine, with a system this large and complex making changes to fundamentals like identities is hard, and done with a lot of care.
All new accounts created today are "decoupled". They are not your Amazon account, and (barring some special internal tools for testing) you cannot make them the same account. But migrating all the existing accounts without causing harm is a messy business.
There is a very large project to fix this. But as you can probably imagine, with a system this large and complex making changes to fundamentals like identities is hard, and done with a lot of care.
All new accounts created today are "decoupled". They are not your Amazon account, and (barring some special internal tools for testing) you cannot make them the same account. But migrating all the existing accounts without causing harm is a messy business.
My own AWS account has the same problem.