Simple answer, cos if the ATCO didnt say it and get a readback then they would get their a
ses kicked by their Local Competency Examiner.
Most ATCO's would agree with you that it is unecessarily verbose and time consuming but the rules are quite clear. Where "Runway Ahead" markings exist on the taxiway then a specific clearance must be given and read back for that portion of the taxi. The reason the "Runway Ahead" markings exist is part of an initiative to help reduce the number of runway incursions which was showing a marked increase before the initiative was introduced.
Incidentally runway 30 at EDI is used on average for about 10% of landings ( thats not including the increased usage when 06/24 is shut) and that is likely to increase . Also, ironically, given your comments on Schipol clearances, which I know to be true, you can be sure that any KLM crew not given such a clearance will immediatley come back and say " Are we clear to cross the undershoot"