Well... with time, people earn experience and can min/max builds, get more heirloom points and so on.
In fact you can expect something that was ok a few months ago to become overpowered as habits change and people learn to exploit broken features better.
Even the looney tunes axe survived a very long time, because until it's very end there wasn't any char that was fast enough to use it effectively, and very few players were using it.
Now that many 2 handers have gone polearm and I also suspect some throwers, archers that liked the melee part and 1h that lost too much damage with the heirloom nerf to have switch for polearms, some issues arise. Furthermore, we try to promote diversity on the battlefield. Even if polearms aren't overpowered (honestly I think some of them were and still are), everyone shouldn't use them.