Based on... what? Ownership of the electrons that make up that particular number?
Like I said... what is worth less than PAPER money? Electrons. Pure Unicorn farts...
Like I said, no intrinsic value for the entries in the blockchain but the fact those entries are there and immutable has created immutable data use cases resulting in demand. Also a whole lot of greater fools. Also most alt coins are pump and dump. However some alt coin some day will supplant Bitcoin because it will be more robust against brute force or newly discovered crypto weaknesses.