There is probably a lot more driving them to La Pen than the economy.
As covered on the forum, due to the decline of people's access to resources (children are worse off than their parents) people are going to be forced to act conservatively, not due to philosophy, but circumstance. This happened before in the UK during the pre- and Victorian period, when the free-for-all-liberal attitudes of the 1700s combined with other factors led to a massive welfare burden and a population who had limited prospects due to a strain on resources. This produced tough people and inovation and tough people. The wealth they create produced soft, emotional slackers. Right now we are in the transition between the two again.
We also have aging populations, which are more likely to shift to conservative positions and change political affiliation. According to a Gallup survey, 71% of teenagers said their political beliefs were close to those of their parents. The same survey suggests that in aggregate half of teenagers who identify as liberal will end up identifying as conservative in later life. It's a largely one-way street.
Another factor is that leftists (who aren't liberal) have fewer children. In the UK if you look at fertility rates they are highest in the areas where UKIP gets a lot of votes, around 2.3, around replacement in fading Labout working class areas and becoming delightfully low in fake liberal areas. One of the lowest is Islington, the seat of Trotskyite Labout leader, Jez Corbyn and the epicenter of leftist thought at about 1.0 fertility rate. This is only by area, you can presume in these areas people who are conservative will be pushing above 2.3 and those who are leftists closer to 1.5. See here for a delve into fertility-rate by political affiliation.
As touched on above, you also have the phenomena of the left being the most sterile, authoritarian and increasingly absured. This is attracting the young. And among the older, increasingly they are leaving the left on a single issue. It's insanity. The left's insanity is one of our biggest assets, because most people who consider themselves left are moderate or have mistaken the left as liberal.
Then you have the increasingly obvious civilisation threatening problems of immigration, which becoming glaringly defined in government statistics from several countries that haven't banned them.
The only thing the left has got for the next few decades is immigration. It's no surprise then that Marcon and Corbyn have essentially called for open borders, the socialists in Germany have suggested giving all immigrant the right to vote, which they already do in Sweden.
As long as immigration is controlled, the left will have no option but to move towards more conservative positions. If its not, we'll be living in very different countries with the rich increasingly retreating into gated communities.