The Commander Rules Committee declared the banning of Hullbreacher today in its July 2021 announcement.
Since the release of Commander Legends, players have bemoaned the play pattern of Hullbreacher in conjunction with “wheel” effects that cause all players to discard their hand and draw a replacement hand resulting in all other players ending up with no cards.
This is the reasoning the Commander Rules Committee used to justify the banning:
There remain a few similar cards that are still permitted, notably Notion Thief and Narset, Parter of Veils. The additional hoops required (an additional color pip for Notion Thief, and sorcery speed for Narset) appear to be keeping them to the appropriate level of play, though we’ll continue to keep an eye on them.
Other news items in the announcement includes the addition of Elizabeth Rice and Kristen Gregory to the Commander Advisory Group and the adjustment of a rule that came up to the complexity of dungeons living in the Command Zone but not being actual cards.
Parts of abilities which bring other traditional card(s) you own from outside the game into the game (such as Living Wish; Spawnsire of Ulamog; Karn, the Great Creator) do not function in Commander.
Read the article from the Commander Rules Committee.