Just terrible conditions. It is really cold, but not QUITE cold enough to turn rain into snow (snow would be much more manageable). So you are soaking wet and just get chilled to to bone the entire time.
Then you add on a relentless headwind. Like, a straight headwind. 25-30 mph.
I've never seen a major marathon - until today - where most of the top contenders decided to wear running jackets the entire way. Their choice was either get hypothermia or add massive wind resistance into 25 mph winds.
Honestly, just standing in full waterproof gear to watch was very unpleasant.
In the face of it, there were some impressive performances across the board. Results are still trickling in, but just all credit to everyone who ran.