If you write a project, you probably won't change the database. But you may add new data layer services such as a cache backend, a search engine with, a secret

If you write a project, you probably won't change the database. But you may add new data layer services such as a cache backend, a search engine with, a secret server, a session store, a permission micro service, etc. They will all interact with permissions and change where you source the data from. Then there is the case where you don't write a project, but a lib. Or the case where you extract such a lib from a project. In that case, you limit the use case of your lib to your database. Because if you don't change database during your project life time, the users of your lib may start a new project with a different database. This is why Django ORM allowed such a vibrant ecosystem: not because it allows changing the data base of one project (although it's nice to have and I used it several times), but also because it allow so called "django pluggable apps" to be database independant.