Without seeing it in person, those lines look like filled compound paths, not a single path with a stroke color. (Results from doing an auto-trace on what I call a “Coloring Book” image…one that has lines but no fill color at the time it was originally traced.)
Quickest thing to do is rasterize them, then use the tutorial below to create a Centerline Trace. Once you have a Centerline trace result, you can set a stroke color and it will be scorable.