To replicate issue

Render using a profile:

quarto render --profile narrow-body

This creates _narrow-body as expected, and _narrow-body doesn't contain _site as expected.

_narrow-body/
├── about.html
├── default-layout.html
├── default-layout_files
├── index.html
├── search.json
├── site_libs
└── styles.css

Now render without a profile:

quarto render

_site now includes _narrow-body:

_site/
├── _narrow-body
├── about.html
├── default-layout.html
├── default-layout_files
├── index.html
├── search.json
├── site_libs
└── styles.css

Problem seems to be adding the file default-layout.qmd - delete this file and there is no unexpected behavior.