I'm sure some of it has to do with operating within the North Atlantic Tracks. Essentially when you lose radio connection you are placed in a slot with a specific speed, bearing, and altitude without the ability to be in constant contact with FAA radio guidance. - the airspace is more congested than you might imagine.

https://en.wikipedia.org/wiki/North_Atlantic_Tracks

expanding upon my above: this article is neat. https://aerosavvy.com/north-atlantic-tracks/