When the World Heritage List was conceived in 1972, its intention was not to spotlight potential tourist destinations. It was to preserve and protect places "of universal value to humanity".The article points out that many of the sites are relatively unknown.
Of course, fame and importance are not equivalent, and as the previous two postings have pointed out, there are important cultural sites that are unrecognized even in their own countries. Global recognition of the importance of a site may help local people to value it more.
A government proposing a site for inclusion on the list is offering a guarantee that the site will be protected and maintained permanently if approved. That of course is a good thing, it the commitment can be fully honored.
Still, one wonders whether some kind of system might be useful which differentiates sites as transcendent as Yellowstone and the Grand Canyon from other (worthy) sites such as Serpent Mound.