It's not the power, it is the individual components of power - current and voltage.
The characteristics of the contacts determine the current rating of the relay. Contact material, shape, and pressure affect how much current they can pass, and can break open repeatedly without degrading prematurely to the point where then cannot conduct any current at all. This is why small signal relays have gold contacts (no corrosion even under light pressure) and high current AC power relays have silver-based contacts (lower resistance/lower heating, and the arc that forms when the high current is broken helps "clean off" oxidation).
In your case the problem is the voltage rating. When open, the contacts are too close together for that high a voltage; it will arc continuously across the gap.
Change your way of thinking: A relay does not switch power - it switches a current at a voltage. Neither rating can be exceeded.