FRA to MUC is only a 2hr 45min drive down the A3-A9 Autobahns with the cities of Würzburg, Nürnberg and Ingolstadt inbetween, less time than it takes driving LHR to MAN. Stuttgart is a similar distance between FRA and MUC.
Frankfurt is a banking and services hub similar to London, Munich is more industrial and similar to the surrounding area of Manchester. LH can make 2 hubs work, why can't BA?