There are a number or reasons, to be fair. Not least the [various]government decisions to 'centre' things on Leeds like road and rail transport which leaves leaves Bradford, which has around 500K inhabitants within the region, on a branch line and which gave Leeds a direct motorway link to London and left us in the doldrums for many years until the M62 joined up to the M1.
In the eighties, Thatcher made Leeds a 'development area', whilst simultaneously ignoring Bradford and clearly not caring about the effect this status for the city ten miles away, would have on its immediate neighbours. Which effectively meant many firms left Bradford for Leeds just to get all the government handouts which came with development area status.