Because it’s a separate template with simpler feature requirements.
Most nav presets don’t point to it.
Most customers don’t land on it.
Most merchants don’t even know /collections/ exists as it’s own stand alone page.
If you need this customization you can contact me for paid services.
Contact info in forum signature.
ALWAYS please provide context, examples: store url, theme name, post url(s) , or any further detail in ALL correspondence.