This seems to me more like simplistic attempt to quickly find the reason.
In my poorer corner of Europe we vote for these "anti-system" parties for more than decade. One could argue that they actually are the system.
I think it was already 20 years ago when a French sociologist whose name I have forgotten showed that the share of vote for the Front National clearly correlated with various negative economic variables, including "distance from the closest still functional railway station".
FYI I don't believe in "THE REASON" or "THE CAUSE" and I am wary of people who reduce complex issues such as voting patterns to one single root cause, but to deny that economic hardship is a significant factor in anti-system vote seems to be wishful thinking to me.
Show me a relatively rich neighbourhood or voting district (say, over 130 per cent of average national GDP) with above average anti-system vote share, anywhere in Europe. I don't think you will find it. People who have a lot to lose don't rock the boat.
The liberal elites are paying for their inability to keep the societal compact somewhat alive. If too many people don't have jobs and can't find a dentist, they will start a "voter disobedience".
Of course the second order effects will be huge, but it is, in a sense, necessary development. A democratic country has to be able to keep a majority of its people reasonably satisfied and well-off.