Hip Hop completely dominated the album charts in 2018.

12 of the top 15 of the best selling albums of the year were from Hip Hop artists, with Drake's Scorpion at number 1 with 3,692,000 sales plus streaming and Post Malone's Beerbongs and Bentley two with 3,046,000 SPS.

Check out the top 25:

As you can see, Hip Hop's strength comes from streams, not traditional sales or downloads. J. Cole has suggested that some of those streams are fake. Even taking that into account, it's pretty clear Hip Hop was the most popular music genre in 2018.