It's a multi use trail and one of the uses is an occasional music concert. Is it a minor annoyance? Yes but the emphasis is on minor. The rest of the trails, both paved & unpaved are open. There's room for everyone.
Well given that cyclists aren't allowed to disturb the concerts that take place at the ampitheatre plopped right in the middle of the west side trail, I don't see much point in worrying about building a trail around the south end of the lake. I think the idea of a trail completely circling the lake was killed when they built that ampitheatre. My two cents.