“Fads” imply sophisticated social interactions that are generally associated with near-human levels (or at least likeness) of intelligence. I interpret that conclusion as being supportive of the idea that these are incredibly intelligent animals, not the opposite.

I'm just saying "fads" implies there's no generally specific reason for their behavior outside of the learned social behavior.

When it comes to other mammals, there's this Human Supremacist mindset that since we can't converse with them, they are incapable of intent / complex thought / problem solving activities.

Humans have been piloting boats across the Atlantic for around 800 years (beginning with Greenland), and the great cod collapse happened on the quincentennial of Columbus's voyage. Each of your explanations has a "why now?" caveat. Fads fit in the gap, unless they've recently developed weapons.

"why now?"

Increasing water temp, climate change, food scarcity, environmental pollution, desperation, habitat loss, new audible or physical disturbances caused by these boats. I mean, there's probably 100 different reasons you could think of for why now.

"Fads" answer nothing aside from simply removing the need for further explanation. Why are they doing that? I don't know, they're bored! It's a fad. Great research.

Orcas enjoy pinning whales and entering the mouth to remove the tongue, even if they do not eat the rest. Perhaps rudders and boat undersides with similar shapes inspire the same play instinct.