A VG lying on the ground becomes an MEL problem...............A member of the flight crew lying on the ground, with a broken arm, leg or head, becomes a possible show stopper.
Very dangerous practice getting onto wet or frozen wings, especially if the paint has been treated with a "protective" coating.
Then there is the problem of clearing the top of the fuselage and horizontal stabilizer without suitable steps, just pay the money and get the job done right!
Tony