Window cleaners are ten a penny JB, but I would imagine a Sky Engineer would have had some training and that costs money. Just Sky looking after their investment…
The aerial riggers at Radio Rentals (back in the day) were supposed to screw a hook into the facia board and hitch the ladder onto that. Not sure if all of them did it though.
I think that a brick would be more secure than a fascia board.
Also don’t overlook that accidents can and do happen. Should a Sky engineer be unfortunate enough to have an accident no doubt any future insurance claim on the company’s insurance would be subject to Health & Safety rules having been followed.
Plus of course your comment about window cleaners being ten a penny. Maybe their insurance is so costly that they take their chances rather than paying the high premium. 
True …but screwing into the fascia is what our riggers used to do. All water under the bridge now.
In those days facias would have been sturdy timber ones and would have been quite secure with a couple of decent hooks…
I think the fixing was to stop the ladders falling as much as for the safety of the riggers. Just enough stop the wall ladder kicking away when transferring onto it from the roof ladder. Also to stop the ladder blowing over if the day was windy.
Transferring from the roof ladder to the wall ladder was an action that always made me nervous. All you can see on the way back down the roof is the ends of the ladder sticking above the guttering. Some of the houses required triple-extension ladders, so quite high up.
I had to do a bit of aerial rigging as part of my apprenticeship. This was before any fixing of the ladders was recommended.
Mart, My legs went funny reading that, especially the bit about transferring from the roof ladder to the wall ladder…
Yet, l’ve seen men in the past, walk on the ridge of a roof, as if they were just walking normally on the ground… eeeek!
I think it’s just what you get used to Art. The aerial riggers who had done the job for years used to walk around on roofs with confidence. They laughed at me because they knew my bravado was hiding the fact that I was a bit scared. I think they could tell by the way I kept trying to use the tiles as handles …and anything else that was within reach. 
Well, I was only a lad and not used to being around chimney pots.
The riggers had ‘riggers mates’. Taken on as school-leavers mostly. After a year or so at the job, they showed no worries when working at heights.
I feel a bit embarrassed that I, too, feel nervous climbing down from our conservatory gutter on to the top rungs of my ladder, and that’s no more than ten feet high.
I believe that Parachute Regiment members think nothing of jumping from that height during their training.