The idea behind Gathering Storm is to make the natural disasters a part of the decision making process, and not just an arbitrary random event as in Civ IV Beyond the Sword. You choose to settle the floodplain or the land around the volcano to reap the benefits, and suffer or manage the occasional disaster as a tradeoff.
Earthquakes have the problem of a) not being tied to a meaningful feature on the map (continental boundaries exist, but there’s nothing special about settling on the boundary itself), and thus b) not having a good enough tradeoff to make the danger anything more than a nuisance.