A loop cut is defined as an edge loop, i.e. a chain of connected edges where each edge shares a vertex with the previous edge, and that vertex has exactly 4 edges attached to it. It works best in a topology of quads, and your mesh is a lot more complicated. I suggest you separate the 'fingers' of your topology by adding edges, and take it from there.

A loop cut is defined as an edge loop, i.e. a chain of connected edges which separates two neighboring quad loops. It works best in a topology of quads, and your mesh is a lot more complicated. I suggest you separate the 'fingers' of your topology by adding edges, and take it from there.