It might be less about it carrying anything specific and more about who owns it or where its headed. This is part of an effort by the houthis to put pressure on Israel to allow humanitarian aid in (their declared reason at least)).
Most of the ships they target are either own fully or partially by Israeli companies, or are headed to Israeli ports
It doesn’t matter that some ships weren’t nominally owned by Israel but in reality owned by shell corporations in turn owned by Israel-supporting billionaires.
Do you have a fact source or just vague associations? The statement at question is "Most of the ships they target are either own fully or partially by Israeli companies, or are headed to Israeli ports"
From source Wikipedia, this is not true. Only 3 of 17 have Israeli ownership or ports of call. Do you have a source for Israeli ownership or ports of call for 6 more ships?
Also, your stated class of "owned by Israel-supporting billionaires" is moving the goalposts. That is not the announced Houthi criteria.
The “goalposts” are defined by the Houthis and unless you think they’re careless or have ulterior motives compared to their stated aim of stopping the Israeli genocide of Palestine, then there must be other reasons they have. For one I’ve heard they take action if a ship doesn’t respond to their hails.
My facts were from various Twitter posts - I don't have them on hand but you can search fairly easily. It's pretty clear that wikipedia data doesn't cover this level of detail - but using game theory - it's pretty reasonable that the Houthis have a political goal and being random or scattershot in their attacks would dilute that goal.
Swan Atlantic has Israeli connections as well from the Wikipedia list. Clearly this list is being updated as info unfolds. Also the lack of a link on the Wikipedia page does not mean there is no link, and just as you missed Swan Atlantic (and I didn't even go through the full list), there can be other ships with Israeli connections that you didn't catch (or entries that were updated since the time you checked)
Do you have a single fact source that differs from the Wikipedia list?
As far as I can tell Swan Atlantic is owned by a Norwegian company without Israeli ties and had no Israeli ports of call. That means the observed Houthi behavior is still 14/17 (82%) not-Israeli-related.
The Houthi behavior is significantly different from Houthi claims of motivation.
It sounds like the ship itself is still intact, which is not too surprising given how absolutely huge they are.