Inertia was designed for development teams who typically build server-side rendered applications using frameworks like Laravel, Ruby on Rails or Django. They create controllers, get data from the database (via an ORM), and render views.
This means building a REST or GraphQL API. It means figuring out auth for that API. It means client-side state management. It means setting up a new Git repo. It means setting up another hosting account for the API. And this list goes on. It's a complete paradigm shift.
This simplicity does create a tight coupling between the back-end and the front-end, but that's already an accepted practice (and arguably a benefit) when building classic server-side rendered apps.