Seems like you haven't looked at the wiki. If you had you should have seen the disadvantage given in the picture.
Because its nearly impossible to monitor an entire playerbase worth of VOIP. If I report you for saying a racial slur, How is IS going to confirm that? Are they then going to have to record your coms? Will they passively record it, and if you get reported save the last 5 minutes? If an entire guild is salty over a raided caravan and reports the other guild leader, how does IS confirm? 20x reports must be accurate right? I am 99% against a VOIP. A Guildchat is mostly unneeded, as they will likely be in discord. Party/raid chat is awesome. 90% for that.