Because there wasn't any. Zeppelin became a non-entity once they officially called it quits and with solo work from Robert, there was no thought of a future. Then 'The Honeydrippers' came and was HUGE, mainly because of Plant and Page together again. Then Live Aid a couple of years later started the whole reunion tour thing all over again. From that point on, it has been obvious how much Zeppelin is still loved, respected and wanted by music fans around the world.
So proud to have been a Zeppelin faithful fan for many decades (one short of seeing them together ), especially right now with the current revival and honours being received.