I don't think it's even as coherent as that. It usually just boils down to vets trying to apply their country's rules for resident dogs to non-residents, without giving any thought as to whether it makes sense.Yes, I don't think it is an EU rule at the moment, just something issued to vets within certain countries for reasons of their own. There's such an obvious difference between the response of vets in France compared to other countries that it has to be the case. They are happy enough to certify the worming and administer vaccinations on request so it can't just be them being awkward and taking against Brits.
While EU Reg 576/2013 is in force there can be no requirement for residency in order to use an EU Pet Passport. All EU countries have to apply that Regulation in the same way. If there is to be a future residency requirement it will occur when EU 576/2013 is replaced by EU 2016/429 on 21 April 2026. At the moment that Regulation has no direct replacement for Article 27 of EU 576/2013. If there is to be the same derogation it will appear in a 'delegated regulation' - one that consults expert groups from each EU country in its formulation. If the expert groups include French vets ........ who knows?