Yeah, they explained that in "PARALLAX", I believe, that the holodeck's power matrix wasn't compatible with the rest of the ship.
Which still never made sense... why have a major power hog be incompatible with the ENTIRE rest of the ship? It's like building a ship made entirely of Lego blocks... except for one Duplo piece.
Yeah... no. And it's still drawing power from somewhere, right? Clean coal?
Someone wanted that holodeck operating NO MATTER WHAT, either in-universe or out.