It's because there was no good reason, other than short sightedness and listening to the wrong people. Keep in mind that DRK has two line aoes in Flood of Shadow and Shadowbringer and Abyssal Drain is a target aoe. Are they also going to reduce those to point blank circle aoes because people were complaining that it wasn't hitting all the mobs in an aoe? Kind of ironic that DRK has the most options when it comes to aoe variations.

It's not a bad change but highly unnecessary when given the large amount of circle aoes WAR already has access too. Some changes that would have been preferred imo:

-Change both overpower and mytrhil tempest to conal aoes
-Change conal aoe from 90 to 180 degrees
-Change hitbox of the vertex to be slightly behind the player as opposed to dead center.

Ultimately this just shows how little faith devs have in the playerbase to allow them to overcome challenges. If you don't like conal aoes, guess what? There's already three (possibly more tanks in the future) other tanks that have circle aoe combos. When did this simple idea of diversity become vitriolic game design? Sadly I expect more of this to happen in the future.