The author's trying to rebut the court's denial of horizontal effect for directives, but I don't grasp his emboldened rhetorical question. The answer's yes. But so what?
Robert Schütze. European Union Law 2 ed. 2018. p 98.
The absence of horizontal direct effect was confirmed in Dori.102 A private company had approached Ms Dori for an English language correspondence course. The contract had been concluded in Milan’s busy central railway station. A few days later, she changed her mind and tried to cancel the contract. A right of cancellation had been provided by the European directive on consumer contracts concluded outside business premises,103 but Italy had not implemented the directive into national law. Could a private party nonetheless directly rely on the unimplemented directive against another private party? The Court was firm:
[A]s is clear from the judgment in Marshall … the case-law on the possibility of relying on directives against State entities is based on the fact that under Article  a directive is binding only in relation to ‘each Member State to which it is addressed’. That case-law seeks to prevent ‘the State from taking advantage of its own failure to comply with [European] law’ … The effect of extending that case-law to the sphere of relations between individuals would be to recognise a power in the [Union] to enact obligations for individuals with immediate effect, whereas it has competence to do so only where it is empowered to adopt regulations. It follows that, in the absence of measures transposing the directive within the prescribed time-limit, consumers cannot derive from the directive itself a right of cancellation as against traders with whom they have concluded a contract or enforce such a right in a national court.104
This denial of any direct effect of directives in horizontal situations was grounded in three arguments.105 First, a textual argument: a directive is binding in relation to each Member State to which it is addressed. (But had the Court not used this very same argument to establish the direct effect of directives in the first place?)