Why is Aurelion Sol so unpopular?

He's very challenging to play effectively, requires very good positioning, and doesn't really have the most enjoyable kit ever designed. It's fun for some, but not really for everyone.

He doesn't even have a good keystone to use. If they buff Phase Rush i think we will see more ASol, still a small amount though.

Simple: Too many Fighters and Assassins Asol cant do shit about.

U dont believe me? Play Asol against Akali, Zed or Yasuo and see for yourself :D And that is just the tip of the iceberg

He takes too much to play effectively and even if you achieve that you feel like you're useless because his kit doesn't provide satisfaction when used properly by the player