I'm not really sure that all dogs need to have their anal glands checked. Obvs if there are symptoms, or if there is a history of blockage, it is important. But perhaps not for other dogs
For the most part, my dog just sees a vet for his annual jabs, and that is the point at which the vet does what is necessary in terms of an 'MOT'. And I don't think he checks my dog's anal glands.
While some dogs do have a vulnerability and need their glands maintained by humans, I suspect that for some dogs there is intervention that isn't very helpful - perhaps from groomers?