I prefer the terms "filch" or "dispossess", not "seize", because:
[a] "senior U.S. official told The Associated Press that no military force was used in the seizures and that the ships weren’t physically confiscated. Rather, U.S. officials threatened ship owners, insurers and captains with sanction to force them to hand over their cargo, which now becomes U.S. property, the official said."
"The US definitely bullied this crew into surrendering and now owns the boat and oil"
I read U.S., Iran Approach Showdown Over Oil Tankers Headed for Venezuela, which suggested that the fact that the tankers were headed to Venezuela was relevant, but it drummed up (pun intended) this question — Why does the US care if Iran meddles in Venezuela?
The United States "will not tolerate continued meddling" by Iran in Venezuelan affairs, a senior Trump administration official told the Washington Free Beacon, bringing nearer the possibility of a naval confrontation between the United States and Tehran over its shipment of oil to the heavily sanctioned Maduro regime.
Five Iranian oil tankers are currently making their way to Venezuela, where they intend to bust an economic blockade established by the Trump administration on President Nicolas Maduro, whose regime has teetered on the brink of collapse since the United States deemed him the country's illegitimate leader and placed a bevy of sanctions on the regime. The tankers included in Iran's fleet are already subject to U.S. sanctions, as is the oil transported on the ships.Recent Stories in National Security
The situation puts the administration in a tight spot: Either it enforces its "maximum pressure" campaign on both nations or avoids sparking a wider military conflict in American waters. President Trump has been clear about his intent to enforce the Monroe Doctrine—a policy of not permitting foreign nations to intervene in the Americas—but he has not yet been confronted with a high-stakes challenge from hostile regimes so close to U.S. soil.