Blizzard will be removing specific engineering items from use in Arenas, starting with Season 1 of WotLK Classic, and they discuss the reasons behind the decision below.

Arena (Source)

Hello again!
We’ve reviewed the engineering items, gathered feedback, and taken a closer look at how certain items and enchantments interacted during the original Wrath of the Lich King. Additionally, the Nitro Boosts enchant can introduce a big advantage for the players that have them as you mentioned, while at the same time, it has the capacity to randomly backfire, which can introduce an unfair loss of rating. For original Wrath, the dev team tried different iterations and still decided to just remove it. So thanks to your feedback, and in the spirit of the competitive nature of ranked Arenas, we will remove them from Arenas starting with the first season of Wrath of the Lich King Classic.

We’ve decided that the following Engineering enchants and items won’t be available for use in Arenas in the first or any season of Wrath of the Lich King Classic:

Gnomish Lightning Generator

Nitro Boosts

Gnomish Net-o-Match Projector (BC item)

Hyper-Vision Goggles (BC item)

Thanks again for all of your feedback. We look forward to seeing you in the Deadly Arenas!