As opposed to being famous based on merit. The Mona Lisa is the most famous painting in the world despite not being all that remarkable, at least by pure aesthetics.
It is made by one of the famous and influential person in history. It is aesthetically pleasing, a bit mysterious yet accessible. The technique is interesting. And with the 1911 theft, it comes with an exciting story.
Taken individually, none of these qualities are that remarkable, but it is the combination, and a bit of chance.
For me there is a mystery and secret in the Mona Lisa which doesn’t exist in other paintings that might show great “skill” and in the end, art is about emotional impact, not what some critic thinks is “skillful”