

More risk to the US personnel or assets, and it would be a diplomatic and domestic incident if it came out that US troops or assets were operating in Yemen. It’s much safer to bomb them from a plane.
Also there’s the terror aspect where the US government presumably wants to cause chaos and fear explicitly to make continuing the blockade less appealing to both the Houthis and the people of Yemen.
If the choice is “be an acomplice to the destruction of an entier country and it’s people” and “don’t get a discount code for college”, like, surely we can see that’s not really a good excuse.