Honest question here: why don't they target the operators for the nameservers that own the affected domain, basically the TLDs?

Oh right, the blocked domain is probably not a french TLD...

And what is your proposed solution to that? It takes minutes to move a service to a different IP, this is a gigantic whack a mole

Well, they might be able to go against the domain registrars and possibly cloud providers that also operate in the french market. But those companies probably have a bigger expensive legal team, while quadnine is just a little non-profit.