Well you’d need facilities and contracts at both airports. Two sets I assume would mean two costs. You need staff at both destinations. You can no doubt get a better deal at one place being served by four flights a day than one flight at one and two or three at another.
Very few long haul carriers split their London ops. Most that do, did it fairly big with multiple daily flights- Emirates, Qatar, BA and Virgin. I think CX was one of the few that split ops with just a daily flight at the second airport.