There are lots of reasons for that, but often it’s to stop the hundreds of candidates from the Philippines, India and Pakistan who apply for every job needing to be responded to.
That was not a casually racist comment, it’s an accurate observation.
Also, it’s usually impractical for people to consider relocating for a low paid job, especially when there may be more than enough perfectly good candidates on the door step.
If you know you are perfect for the job, send a CV without an address (all recruitment agencies leave the address off, as well as salaries and those corny hobbies and interests bits) but with a powerful short and personalised covering note. Just give a mobile number and deal with the location issue once you have got the job offer.