It looks like the cancellations are:
2104: 07:55 from WAS
2121: 14:00 from NYP
2128: 20:10 from WAS
2175: 21:12 from NYP
All are weekday only trains. It's a little weird to do this for low demand, because 93 and 19 (adjacent to 2121) are busy and can be difficult to get a decent price for a seat on. I can speak to around 8:00 out of WAS. I can see where late night would be better attended by the Regionals. There's no denying the Acela recovery has been lackluster, but we're back to capacity problems on the NEC. Tomorrow 176, 184, 20, 80, and 90 are sold out WAS-NYP and 51, 91, 19, and 97 from NYP-WAS (though 91, 97 still have seats for long hauls). I think something may be going on here besides low demand. Maybe equipment problems?
Edit: Maybe staffing? At this point with so many regionals connecting to state services, it is probably easier to cut Acela trips, especially if margins aren't what they once were.