They can't help themselves.
I find the Mélenchon position interesting though. I'm hearing a lot of people on the left (soft and hard) condemning him for not endorsing Macron. From my position, were I French, I would vote Macron next weekend, but with a clothes-peg clamped over my nose. He stinks of the complacent, EU-knows-best, centrist, elitism of the likes of Schäuble, Dijsselbloem and Juncker; the ones who got the EU into the mess it's in now, who pay lip-service to subsidiarity, but implement it not one iota. I could be wrong and he could be the fresh wind that blows the corporatists away, but I doubt it. If it weren't for the anti-semitism and the Islamophobia, I'd probably vote FN too, but take those things away and Le Pen's nothing but a nationalist syndicalist and wouldn't have a neo-Nazi base to do her leg-work. She'd get my anti-establishment vote and lose a hundred xenophobes'.
So, Mélenchon says "not a single vote for Le Pen", but doesn't say, "Macron's the one!" I could live with that, but the liberal centre and centre-left cries foul. Typical. It's like Nick Cohen and Peter Mandelson are speaking French, albeit heavily accented.