It was very easy to go from one job to the other. weather it needs to be required or not, many jobs today effectively require 20 years of education (12+ school, 4 undergrad, 2 masters, 2 years experience).
we talk about coal mining jobs going away as if they should have seen it coming, but tech can also be vulnerable. people forget what it was like to search for a tech job even years after the 2001 bubble burst.
also, the reason why people are worried about automation isn't the number of people effected by each iteration. it was widely accepted automation would destroy jobs and more than what was destroyed would come.
the 2001 and 2008 recession seems to indicate that is becoming less true. i would categorize those recessions as mass unemployment, thus mass unemployment is not becoming less and less likely.