Why not mandate that all data centers must be completely off the grid instead?

Maybe they will. They are not banning them permanently. They are placing a moratorium until 2027 so they can research and plan for how to do data centers responsibly

> The bill also creates the Maine Data Center Coordination Council, and instructs the council to provide strategic input, facilitate planning considerations and evaluate policy tools to address data center opportunities.

So they install noisy, loud fossil fuel generators that pollute the surrounding area.