That sounds miserable, sorry to hear of the ordeal.

Unfortunately it sounds completely out of BA’s control. I’ve been at EWR during a major snowstorm and ended up being canceled after the de-icing truck could not work fast enough. We were fortunate enough to get a gate quickly as the domestic airlines had proactively canceled most flights.

There are US guidelines to try to avoid situations like this, but I believe they apply to domestic flights more strictly than international flights (3 hours vs 4 hours), but that limit can be extended as needed by ATC.

My guess is that priority was given to departing flights needing to return to the gate to allow passengers to deplane, further exacerbating the issue for arriving passengers.