You do have a point, OP. But I really don't believe that every single one of these people are just deliberately not turning up. I think there's a massive glitch in the system (as a number of posters have said.)
As quite a few people have said, some people get a letter for an appointment a day or two after the appointment. Some people don't get a letter at all, because the department in question didn't send one, OR they sent to an old address they moved from a couple of years ago. Or sent a text to an old phone number.
We've got a mobile phone that we use as a burner phone now that we haven't actually used as a proper functioning mobile phone number for 2.75 years. (We both got new ones in Spring 2020.) Yet at least three or four different departments have contacted us by phone call or text on this number in the last six months. They HAVE our new numbers and sometimes call them on them, but SOMEtimes it's the old one. The DWP, the tax office, the hospital, and the dentist. Although they've got our new number on the computer, they've got the old one we haven't used since early 2020 written manually on our files. In November, the number died through lack of use. So if someone like the hospital sends a message on it, we won't get it now!!!
I do also know a few people who couldn't make their appointments or procedure, so they did contact someone and leave a message - or they emailed. Or sent a text back to say 'I can't make his procedure.' And then about three or four weeks after they got a rollicking from their GP for not turning up.
So I really do think there's a glitch in the system, but yeah, for sure there are some people that don't turn up. My husband went for a specialist appointment several months ago and there were six people due to go in that morning... Only three turned up. The specialist phoned all six people HERSELF three or four days before to make sure they were still coming. One said they couldn't make it. And the other 5 said they can. So that was 5 that was due. 3 turned up.
The system needs overhauling, with a 'fine' to those who confirm they are coming when asked several days before, who then do not turn up!!! They also drop to the very VERY bottom of the list.