"ADV leaders like GS, Super Tenere, Triumph Tigers, Honda VFR-ADV etc all shaft, wonder why didn't they keep chains on those?"
Those bikes are all intended for light offroading like fire and logging roads. They see 90% street and 10% dirt so they are manufactured for more touring than adventuring. They typically won't get into true trail riding and the advantages of a chain are never needed. You'll notice that the lighter more dirt oriented ADV bikes like the GS700-850cc series, Africa Twin, Tenere 700, and all KTMs are chain because you can hit single track trails on those bikes. They are all essentially big dirt bikes that can handle street touring, while the big ADV bikes are street bikes that can handle some offroading.
In the end, I love that my FJR is shaft and that my dirt bike is chain because each fulfill their purpose very well!