Because profits go up, but wages are stagnant. Corporations are increasingly cutting benefits, pensions, and treating employees as contractors and outsourcing. Millennials today are poorer than their parents were. This is the age we live in, profit maximization over everything else. The rich got richer, but the middle class and poor haven't seen any of these gains. Why should anyone believe that anything would change otherwise?
Even the unemployed people will gain in the long-term as the gains trickle down and/or they gain from other technological advances.
In the short run, depending on how rapidly automation occurs, this class of people will suffer greatly. They will need to be retrained and educated. It may be worthwhile for the state to invest in its people.
There are always jobs, but people don't take them because the wages are too low.
If the only jobs available are low paying with terrible conditions, then that's not a society you want to live in.
Its convenient to hide behind the economic theories, making sure the graphs line up so we don't see any deadweight losses or inefficiencies. But the practicality of it is always a shade darker. People cheat, monopolies are held. Gains don't always trickle down.