"This video is not available in your country"
Region blocking is set by whoever owns the content, not by YouTube. That explains both why it happens and why there is rarely a way around it.
Who blocks what, and why
Music, sport and television are usually licensed territory by territory. A label may hold the rights in one country and a different company in another, so a video can be published in one place and withheld in the next.
Uploaders can also restrict a video themselves, and occasionally a national regulator requires a block. In all of these cases YouTube is enforcing someone else’s decision.
Why a download tool shows it as unavailable
A download service reads the video from its own servers, in whatever country those servers sit. If the video is blocked there, the service sees exactly what a visitor in that country would see.
This is why the same link can work for one person and fail for another, and why trying again later sometimes succeeds — a request may be served from a different location.
What actually helps
Often the same material exists on another channel that published it with wider rights. Searching the title rather than reusing the link is the simplest fix and frequently works.
The official channel for the artist or broadcaster in your own region is the next place to look. Beyond that, a regional restriction is a licensing decision, and there is no technical setting on our side that changes it.