They're mostly youngsters doing it for minimum wage
The reason you have markers is because the majority of shooters can't be arsed to do it themselves
If some shooter can't get them on the board then why should the onus of responsibility fall on the marker?
Those frames at 1000 yds are 12'x6'....that's barn door size, if your shooter can't then hit that proverbial barn door, then does he really have business trying? especially if he has to be withdrawn and sent to the zero range to confirm everything!
I was at Bisley yesterday, and we were having enough trouble at 600.....1000 is a totally different story
For the record, the backstop on Stickledown is 100 yds behind the target, so it is very difficult to gauge and relay fall of shot