Global chats get too many hot takes and inappropriate chatter anyway. You can see this in areas where people use shout chat a lot such as Ul'dah on Balmung.

Although this happens in the Novice Network sometimes, especially by crafter/gatherer mentors, the filtering involved does help a lot.

Linkshells are usually dead because there aren't enough people allowed in them.

The Novice Network strikes the right balance by filtering people to an extent and by not having a limit on how many people can be in there overall, just how many can be in there at a given moment. That is different for a linkshell, where it's not a limit on logged in members, but a limit on all members including those that are offline.

No chat is perfect and occasionally there are incidents, but every novice network I've spent time in has been full of hours of answering new player and returner questions, helping them with queues, teaching them things and showing map links for quests they are stuck on. When I look at the novice network I am spending so much time doing these things and so are a lot of the other active mentors in there.