Of course there is a contract. A private one.
What I meant is why -- other than for reasons of minimum wahe, health & welfare -- should it be a STATE-created contract.
Why on Earth is the French Government telling employers what to do with their "Premieres Embauches"?
It's not telling the employer what to do. It's allowing the employer to do things that were not previously accepted, by law, by the jurisprudence. It's saying: from now on, if you hire someone under 26, you're free to fire them at will over a two-year period. This kind of regulation is requested by the bosses' unions. (Though they're backing off from this one now, because it's become a hot potato).
It's not an easy thing to explain without it looking like I'm (me or another) being defensive about a system that isn't necessarily all good (though I must say that Americans can be very aggressive/out-of-hand dismissive about this subject, and that kindles defensive responses). My point, as someone who came from another country with an Anglo-Saxon common law basis, and who had trouble at first understanding what was going on here, is that other ways of doing things exist, and there isn't necessarily a right and a wrong about it.
And don't let me get started about whether it has been demonstrated that the American way of handling contractual relations between employer and employee has been productive of good, equitable results across society. (No, the French way hasn't either, but it does provide lower-level employees with more security, and develops a minimum net of solidarity).