Wouldn't be surprised if there was a connection - having to use the 53 foot trailers to make up capacity because they don't have enough drivers and are taking on the crappy drivers because conditions in the industry are so poor that many just up and quit.
Newer facilities and greater demand. If you can get more freight moved in one trip, go for it. IDK if the train cars that haul the box part have caught up with 53 footers or if they still do 40's for the most part.