The GB wanted all the leadership for themselves claiming to the the FDS so that there wouldn't be any question about whose opinion counts as "doctrine". - Oppostate
To clarify, this change was actually more a means to protect WT assets.
WT's lawyer was forced to testify to the Judge in an Australian court of law, the FDS class is only a theological arrangement. IOW, the FDS class does not actually exist.
It was only after this that WT teachings were changed so that any claiming to be anointed, are no longer immediately included within the FDS, only the GB is.
The GB also changed their doctrine to have not yet inherited Christ's belongings but will inherit them once the Great Tribulation commences.
For additional info and clarification on this, the link below is to Louise Goode and Laura Kaput's JW Community Podcast episode S06E17 'How the Faithful and Discreet Slave were killed' where they interview Steven Unthank.
Steven Unthank interview - Sept 2018