Aside from it making it more cumbersome to the indie artists & small venue/festival market by the rule of having to apply to a government apporved anybody makes it an easy way to streamlined a basis. If it's folk that's seen as a protest music/movement then it's streamlined a way to exclude performers in this genre to enter within it's borders. There were/are many nations that wanted to wipe out jazz or (insert name of the week here) from the clubs & venues within their confines.
Another reason is border reg warfare. When one nation puts up restrictions another nation retalates. Brazil did this not to long ago

Barry