You need housing to support the cable for flexible and bent runs, but not along the frame where it runs in a straight line between braze-on fulcrums (aka cable stops), or around fixed pivot points line the bottom bracket.
So there's no need to cover those bare wires. But the next time you replace the cables you might want to cover them so you won't scratch the frame if. for example, you grab it by a frame tube to carry it.
If you do chose to cover the wire along the frame, cut the cover a bit shorter than the span, so it can move back and forth with the wire and not increase friction by causing the wire to slide within the cover.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.