You saw the “or unimportant” part of that sentence right?
Because people don’t play brawlers to fight creeps. They play brawlers to fight heroes.
Which the majority of HotS doesn’t.
Killing enemy creeps for victory was an organic thing that happened, whether intentionally or just in the course of stomping the enemy team with AoE. When you did it strategically you helped your creeps push into the towers so they can soak cannonballs while you siege the towers. When you didn’t do it strategically the enemy creeps still died and your creeps sieged the towers anyway.
And if their goal was to make it more notable to players then they could have increased the text size to match the popup from killing merc camps, or added the audio jingle to killing creeps. Both things would have fixed the “What dis do” problem without breaking the game design for half a dozen characters, and rendered several dozen others out of their element by forcing them to go melee when they aren’t designed to be melee heroes.
They’re also more satisfying and impactful to do than AA’ing creeps that pose no danger to you. Murdering creeps for levels is, bar none, the singularly most boring element of HotS, but prior to this change it was a boring element that was easily done without feeling like it was a chore.
Now it feels like a chore.
That’s what ranked play is for. Most people don’t see farming creeps as fun ¯\_(ツ)_/¯