Hmm... the best I can figure out off of Flight Aware is about 650 flights for UAL outta EWR and LGA. Delta has about 560 flight/day out of JFK and LGA. That's about 15% less than UAL.

Yesterday, UAL cancelled 191 flights out of EWR alone and DAL only canceled 27 total from JFK and LGA. That's a 700 % greater cnx rate on about 18% greater volume. If we were talking small numbers it might be that egregious of a disparity due to small sample size, unfortunately 191 cnx out of EWR is significant.

So, it might have more to to with something other than sheer numbers as I take your post to allude to as the biggest reason.


edit ....Sailing beat me to it sort of