It's very possible (probably likely) that I'm wrong, but wasn't the chainsaw drill team made up of the "Fire Crew" on stand by to fill in wherever needed in the event of people calling in sick from the houses/zones? I'm pretty sure I remember reading that years ago. In "regular" years, that might be a set amount of people based on historical averages so they could be confident in having enough people to staff the "unofficial zone". This year, with the 1000lbs gorilla in the room looming over the event, maybe they don't have that luxury of having a reliable amount of scareactors available each night.
Could they hire 30 more people to staff two shifts for the zone? Of course, but adding 30 people to the payroll of what is arguably a reduced capacity year (international travel restrictions and people wary of heading to Covid Town, USA from other states) while already trying to earn back "lost money" from last year is a hard sell. And if they are having issues filling concessions and the like, plus Howl O Scream opening right down the block "cannibalizing" talent, is there REALLY that large of a talent pool looking to do it for the entire run?
EDIT to add that sounded confrontational and I didn't intended that at all, was pretty much debating with myself if I remembered the cast correctly and wondering if there were that many people looking for seasonal employment until 2am when the parks are having trouble staffing regular day shifts. I know being an HHN Scareactor is a desired job for many so am honestly curious if there are people waiting for a call to come in.