Another fact is the older a video game becomes, especially a competitive one, the higher the average player ability. Sooner or later not-so-good players figure out it's not worth wasting their time on and leave the scene, because yeah winning is fun and losing is not.
Ratings are not based on absolute skill, they are based on relative win/loss chance compared to the rest of the player base. Your 1500 rating is roughly average but that also says something about the strength of the players still playing.