https://oppositelock.kinja.com/tow-me-d ... 1609771499
describes why Europeans tow with small cars while Americans tow with large trucks.
In the first setup, the tongue weight is higher, making it more difficult for a small car to tow. In the second setup, the lesser tongue weight makes it possible for a small car to tow, but worsens stability at high speeds. European drivers need to be much more conscious of staying within a safe speed for towing trailers set up to be towable by small cars.
So do not be surprised if the Ampera-E is rated to tow in Europe with low-tongue-weight trailers at low speeds (as is done with other small cars there). The Bolt presumably has no tow rating because towing a trailer with a low enough tongue weight would be unsafe as soon as the combination gets to the speed of a typical US freeway.