It was probably in Legion when they dispersed all the max level people into every different part of the new continent with World Quests. Having one max level outdoor zone works wonders for world PvP. I remember always seeing tons of horde and alliance killing each other in Tanaan jungle, often chasing each other into the enemy hub.
Generally, world PvP occurs when lots of people get funneled into a zone with limited ressources. However, if everyone is busy doing all kinds of other stuff all around KT + Zandalar, there's simply going to be less people in one place at a time. The game is simply too busy at the moment.
Often times we would do world PvP when we already had our conquest cap and there was "nothing to do". For example, back in MoP a hunter friend of mine and me would wait on the other side of the Ordos bridge with mass grip and explosive trap and send entire groups flying to their deaths. Of course we only did that because we had already completed our share of content for the week. Not being busy in a game like WoW can be a good thing because it allows the player to make up his own ways of playing without having the fear of missing out on gear etc.