application.html.erb never renders

Hey,

My application.html.erb layout is not rendering at all. Its the only
file in the layout folder. I've deleted the public/index.html file.

Whenever i go to http://localhost:3000/

I get the root page view set in routes.rb without the layout. I've tried
adding layout "application" in the application controller but that
doesn't work either. I have to go in all controllers and write layout
"application" to make application.html.erb render smoothly.

Any idea why application.html.erb is not rendered by default?

Best Regards.