soberwp/controller by default only matches one template. AFAIK this is by design. See: How to create a controller file for a custom template page in Sage 9
Matching is done based in the WordPress template heirachy, and only one template ultimately matches. I guess the front page has higher priority than a custom page template?
View Composers in Sage 10 match by blade view file, so they don’t necessarily have the same issues.