I'm confused by this.  K2 hasn't started yet but still charts?  I heard that Moon Lovers was not doing well in Korea yet it's #2 here, so can you tell us where you get your stats?
This is a top based on the search and trending popularity of the dramas in Korea [on Naver & Daum] and not based on TV ratings ... that is why dramas that didn't start airing yet [like 'The K2'] get to be on the top ... cuz are popular in searches and are already trending ...  their popularity is growing even before the first broadcast [cuz of cast, posters, teasers, interviews and other promotion methods] ... 

And yes i'm amazed myself that Moon Lovers has such a small rating on TV ... yet on the Korean Web is one of the most popular ... from it's first airing ... every day of the week it was on top 3 popular dramas ... 

So it's Top 20 Most Popular in searches [trending] Korean Dramas on the Korean Web ... 
★ ★ ★ TOP 20 Korean Dramas September 2016 [Week 3] ~ by Popularity in Korea ★ ★ ★

★ ★ ★ TOP 20 Korean Dramas September 2016 [Week 4] ~ by Popularity in Korea ★ ★ ★

 ★ ★ ★ TOP 20 Popular / Trending Korean Dramas October 2016 [Week 1] ★ ★ ★

★ ★ ★ TOP 20 Popular / Trending Korean Dramas October 2016 [Week 2] ★ ★ ★

@AdoraLee Thanks for your explanation.  That makes way more sense.  Sorry it took so long to reply.
★ ★ ★ TOP 20 Popular / Trending Korean Dramas October 2016 [Week 3] ★ ★ ★

★ ★ ★ TOP 20 Popular / Trending Korean Dramas October 2016 [Week 4] ★ ★ ★

★ ★ ★ TOP 20 Popular / Trending Korean Dramas October 2016 [Week 5] ★ ★ ★


★ ★ ★ TOP 20 Popular / Trending Korean Dramas November 2016 [Week 1] ★ ★ ★

★ ★ ★ TOP 20 Popular / Trending Korean Dramas November 2016 [Week 2] ★ ★ ★

★ ★ ★ TOP 20 Popular / Trending Korean Dramas November 2016 [Week 3] ★ ★ ★

★ ★ ★ TOP 20 Popular / Trending Korean Dramas November 2016 [Week 4] ★ ★ ★

★ ★ ★ TOP 20 Popular / Trending Korean Dramas December 2016 [Week 1] ★ ★ ★