Why does "This video is not available in your country" come up sometimes?

Many times I will go to check out a video on a site like YouTube and I get the message “This video is not available in your country”.

It doesn’t make sense to me that one can be excluded, in this way, especially on the internet…based on the country they reside in. What is the point of blocking a video in this way? I thought that maybe it had something to do with copyright laws in Canada; but, it happens on videos that shouldn’t fall under that.