Subreddit subscriber counts:
r/intel: 52,948
r/nvidia: 176,171
r/amd: 233,031
So, among tech enthusiasts on Reddit, r/AMD has more followers than Intel and Nvidia *combined*.
Obviously that isn't really representative of anything other than Reddit, but nobody claimed otherwise. Certain demographics, those demographics being people who like to argue about PC hardware on the internet.
AMD is, if nothing else, WAY more interesting than Intel or Nvidia right now, so it makes sense that enthusiasts are really into AMD.