Birmingham has always had strong links with Germany and STR-BHX is a niche route having been a continual link since the days of Birmingham European
Its the auto industries that sustains BHX-STR and yes its had a more consistent connection over thirty years than the on/off Manchester route.
Frankly and I do't like saying it but LPL-STR would probably work better from the North West what with Vauxhall and a host of suppliers and the Chemical companies just down the road in Runcorn many working with BASF in Stuttgart and other similar companies