The problem is that the left seems to be completely castrated, achieving very little in ways to actually help the average people, meanwhile the (alt) right is offering the typical fascist approach of simple solutions to complex problems...
Most people aren't economists. They don't, and more importantly, don't WANT to grasp the intricacies of why things are shite and why it takes a long time to fix them. They want their lives improved, without being too involved.
The left has simultaneously failed to market themselves as the solution OR when in power, deliver any solutions.
And it doesn't matter how bad an alt right government would be, people just want to be less tired, have more money, and that's PRECISELY what Le Pen and the rest of these fuckers promise.
The added racism and xenophobia on top is just a little extra to play into people's tribalism - pin all the issues on the immigrants, the foreigners, the people most outside the average person's tribes, and all that fearmongering will play directly onto these promises.
One of the most important challenges, once we beat these fascist pieces of shit, will be the reform to education, so that critical thinking is taught appropriately, allowing people to at the very least recognise the very typical fascist methodology of playing into people's emotions to get away with everything. Because these altright chuds never deliver. But they can always talk their way out of not delivering.