He was the big draw on fox, it not only hurts their over all demographics: they literally cannot replace him in any meaningful way. This is a MAJOR blow to the propaganda, to the endless stream of spewed hate and lies.
Plus, as mentioned: it's a massive wake up call to the cult. It shakes the very alternate reality they've crafted.
And it's not like carlson can go and be in the media again. Fox won't abide by losing their marketshare to the likes of OAN, none of the left will touch him. This is literally the end of tuckers broadcasting career, and a massive blow to the reach of fox. Hell, This ALONE might be enough to knock fox off the #1 nightly news slot.