Yes, "too many people use it".
We had a great service near me which was a walk-in NHS surgery inside the local Boots.
Like everyone, we are registered with our local doctor's surgery. When I want an appointment, I have to wait several weeks or, ring up on the day I need to see the doctor and hope that I can get through given everyone else who needs an appointment is also trying to ring at exactly the same time.
It's a crap service but one we've been brainwashed into thinking is the best way of doing things.
So, my saving grace in the event I really do need to see a doctor (which isn't very often) is that I could drive the 20 miles to the next big town and see a doctor at the walk-in surgery. I might have to wait an hour or so but it's not much more difficult than that.
I googled the opening hours today only to find out it's closed down because it was too popular and people were using it as an "alternative to the practice where they were registered". Yes, they were because they can't get a bloody appointment at their local practice unless they are prepared to wait 3 weeks or more.
I've tried for 8 consecutive days to get an appointment for my DD at the local surgery. The doctor was on holiday, then off sick. Now I have to sit in the queue with all the other hopefuls. I was told she should sit outside the surgery in the morning and insist on seeing a doctor right there and then. She's 16.
I don't even want to go into the inefficiencies that have led us to this point but surely it's time for someone sensible to take the reins of the NHS and look at things from a patient perspective. It's driving me nuts.