I mean, isolation transformers like in regular amd PoE Ethernet are a form of capacitive coupling.

The windings in isolation transformers are inductively coupled through the magnetic field in the core. There's often a shield between the two windings to reduce any capacitive coupling.

The industry standard for SPE is moving towards a transformer as well, because to get 1,5kV in isolation from a capacitor requires large components. A transformer is a lot smaller and provides common mode rejection.