The premise of your question isn't really correct.

France suffered from domestic terrorism from diverse sources. There was rightwing domestic terror attacks carried out by the OAS, a terrorist cell dedicated to opposing French withdrawal from Algeria. In 1961, they derailed the Strasbourg-Paris express train at Blacy, killing 28 people - France's deadliest terror attack until the Paris attacks of 2015. In 1986, a far-right group called "SOS-France" tried to bomb the Toulon office of the antiracist pressure grouip SOS-Racisme, but blew themselves up instead. There was also minor left-wing terror groups such as Action direct and the Armed Nuclei for Popular Autonomy (NAPAP). Action directe's most notable victims were General Rene Audran, who oversaw French arms sales, and Georges Besse, the CEO of Renault. NAPAP carried out a series of bombings through the 1970s, although these did not kill anyone, and also murdered Jean-Antoine Tramoni, a former security guard at the Renault plant, in reprisal for Tramoni's own murder of the Maoist activist Pierre Overney.

Alongside political terrorism, however, there was also domestic terrorism from nationalists and autonomists in France's regions. I am not intimately familiar with the process, but quite famously France attempted during the 19th-century to subsume its varied regional identities (Basque, Breton, Occitanian, etc.) into a single French identity speaking a single, standardised, French language - and largely seems to have succeeded. Eugen Weber's Peasants into Frenchmen: The Modernization of Rural France 1870-1914 is a foundational text on this process.

However, that of course led to diverse regionalist resistance, which sometimes took the form of terrorist violence. The Breton Liberation Front and the Breton Revolutionary Army became known as the "smiling terrorists" for their bombing campaign against symbols of the French state and globalisation in which they attempted to avoid civilian casualties - successfully until 2000, when a bomb set in a McDonalds in Quévert killed a 27 year-old employee and collapsed such popular support as they had. In Corsica, the Corsican National Liberation Front (FLNC) attacked government buildings and estate agents selling Corsican properties to mainland French, and later assassinated the French prefect Claude Érignac in 1998. The Basque nationalist group ETA also operated in the French Basque country, using it as a safe haven from reprisals by Francoist Spain and as a place to steal explosives from.