Why does IMDb uses Metacritic?

I don't understand why IMDb uses the Metascore as a reference, since it is so outdated when it concerns older movies.

The Metascore reflects the feeling when the movies were released, not how they are seen today. The Thing, for example, was not well-received by the time of its release, but today is regarded as a masterpiece. So why do you have to put this 57 Metascore rating side by side with the 8.2 IMDb rating, which is much more reliable and up to date? It is only an example, but there is a lot more like that. It doesn't make any sense to show TWO RATINGS, specially when they are so different. Some classic movies get bigger with time, but Metacritic and the awful Rotten Tomatoes simply don't take this under consideration. IMDb should stick only to their own ratings, they are simply better and do much more justice to classic movies.