The problem is that its not a DC connection to the grid.

Not only do you have to match voltage on re-connection, but you have to match frequency AND phase.

Its "doable" but to do so reliably without a stable reference can be challenging. That's why the DC requirement is there. They want some form of reliable power to well tested electronics to match phase and frequency when the grid comes back up.

A heavily loaded AC line will drift in voltage and frequency stability (say when your AC kicks on and browns out your solar panels).