They're called "pup" trailers [1] (example photo [2]), and the very long hitch exists for a few reasons: per-axle weight limit, respecting max weight capacity of smaller bridges, and ease of unloading [3] among them.

1: https://titanww.com/what-is-a-pup-trailer/

2: https://imgur.com/raDJVVL

3: https://www.youtube.com/watch?v=mU5L_2TMjKc (sorry, terrible handheld video)