In a VPLS design solution, why would you use BGP instead of LDP for signaling?

VPLS interworking is a specific niche feature and not the primary architectural motivation for choosing BGP over LDP as the signaling protocol for a VPLS deployment.

BGP route reflectors reduce the number of BGP sessions required between PEs, but full-mesh pseudowires are still required between all PE routers participating in the VPLS instance - route reflection does not eliminate the pseudowire mesh.

MAC address learning in VPLS is a data-plane operation that occurs regardless of whether BGP or LDP is used for control-plane signaling, so the choice of signaling protocol does not affect MAC learning scalability.

In BGP-based VPLS (RFC 4761), BGP carries both the auto-discovery information and the signaling labels needed to set up pseudowires between all PE routers in a VPLS instance. Because pseudowire endpoints are learned and signaled automatically through BGP updates, operators do not need to manually configure each individual pseudowire, dramatically reducing configuration overhead in large-scale deployments.