Even if Stranger Things season 3 went back, it did not dethrone how popular Game of Thrones was during its final season. There are genuinely a lot of people who have become addicted to GoT that they feel that something is missing in their life after the series is over.
People who love Stranger Things love the series but not to the point that they would make an effort to know more about the things that are being advertised in the series. This is very entertaining, but it will take a lot more before it would reach the popularity that Game of Thrones was able to generate over its different seasons.