Is the FN failure to win that surprising? They invariably due poorly in run-off elections. I can remember reading about how the FN was about to win maybe a dozen seats in the 1994 National Assembly elections and laughing about how ridiculous that assertion was.
I thought they were favored to eek out narrow victories in PACA/NPDC (but nowhere else). Regional powers in France are relatively weak and this is a lot different than a high-stakes national presidential election. Voting for the FN in the former does not mean electing Marine Le Pen as President.