>>315560864
CPU has to package all that stuff into a collection of data called a drawcall that gets sent to the gpu to render. CPU is singlethreaded so it all goes in a conga line one by one to the gpu every frame. The more skinned meshes the more drawcalls need to be made and sent to the gpu. Also a skinnedmesh is it's own thing that needs to be calculated. Every frame the skinnedmesh is deformed by the armature bones and the resulting new position of the vertexes are sent to the gpu. Assumption is doing it all in one skinned mesh is more efficient than doing it in multiple.