The ARENH program originated with EU liberalization efforts.
https://fsr.eui.eu/regulated-access-to-incumbent-nuclear-ele...
I read your link and I don't see why you say originated. This is a French law. My understanding is that EDF wanted to take a stake in a German energy producer and to approve such a takeover the EU as the market authority required some type of market liberalization of the French energy market.
France chose to use the mechanism of ARENH. This isn't an EU thing.
It's a French law to comply with EU requirements.
That's usually how that works. The EU makes rules and national parliaments create local laws to comply.
Of course they could have chosen another way to comply, for example breaking up EDF. But they didn't want to do that, probably for good reasons.
ARENH looks like a mechanism by which France wanted to entice competition in end customer sales (and distribution?) of electricity.