What was the purpose of giving Artificer’s something that’s going to be exactly extra attack 99.9% of the time (since they can make their own magic weapon) instead of just giving them extra attack? Were you worried Artificer’s would exploit regular Extra Attack? Playtesting. We're experimenting with a class-favored version of Extra Attack, which ties into the class's theme: magic through objects. Playtest feedback and our own tinkering will determine whether the feature survives in its current form.
— Jeremy Crawford (@JeremyECrawford) March 5, 2019