As a former flat rate tech,you learn diagnostics are 90% of a job.It requires either hard learned experience or diligent studying combined with research skills as to where to find resources.All this adds up to work which seemingly many find too tedious in todays world,whatcha think?
Well that and the instant gratification of a child. They want it now and on a silver platter without all the work. With FEW exceptions, flat rate was all I ever worked under, so you better have some diagnostic skills or go hungry.