The US had designated Austici/Inventati as a terrorist organization and OFAC sanctions before seizing the servers. A terrorism designation is basically meant to strip an individual or organization of their rights. The US government will try to seize the assets of anyone who financially aids an entity on the OFAC list. The Dutch complied with the seizure order because of the terrorism designation. This is also a violation of the law known as 'Section 230', which says that internet services are not legally liable for communications made by their users. The US government could designate Hexbear as a terrorism organization and place OFAC sanctions on Hexbear, but that would be extra steps.