We actually did... Until five years ago.
Long story short, the FN (now RN) always have been the pariah of french politics. When Le Pen father (notable contributor to the OAS and officer suspected to have participated to the coup attempt) managed to arrive in the second turn against Chirac, we witnessed a near stalinian level of elections. Chirac won 80/20 something like that. Pretty much everyone allied against them. And that which we called the "Front Republicain" (the idea that, should they pass, the whole political spectrum would beat them with shoes again) pretty much held until the collapse of the socialist party at the end of Hollande's presidency.
Basically, the two governance parties (right then left) failed quite spectacularly one after the other. The UMP (moderate right) failed and tried to rebrand, then disapeared from the public consciousness. Then the socialist came in power and failed so hard they actually had to sell their offices.
It's a very special moment in the french politcal history, because our anti-fascist dam just vanished and people are still looking for something to replace it.
It'll take time before we have stability again, and that is the opportunity that allows the far right to score (relatively) high.
Edit : And when I mean "high"...it's high for a far right party. 60-40 would be a decisive and humiliating defeat for a governance party in normal times, but we're not in normal times, clearly.