It has mediocre bulk and only 81 base Attack, which means it needs a boost from Swords Dance. Problem is, it has low bulk so it can't set-up. Unburden boosts it's Speed, but it's already pretty high and the boost will only let it ouspeed a few more things. It doesn't work as a good Defogger either. Finally, Ubers are a lot more powerful. Look at Zacian. Its much better. Also, Ubers were used on a lot of teams for them to get kicked out of OU. Hawlucha doesn't see use on a lot of teams and thus isn't fit to be an Uber.