Not entirely sure they were actually in Iranian waters.
Launching from Kuwait and heading south, there is no way, based on tide currents, that these boats would ever stray or drift into Iranian waters (within 3-miles of the Iranian coast-line-—3 miles. . .that would require the boats driving north).
Here is a graphic depiction of the current flows: https://www.youtube.com/watch?v=iZl8fVHWanQ
Perhaps the Navy, always the most sensitive to the political waters (since Tailhook), they are sacrificing a few personnel to make it the fault of the US (Navy) and therefore can’t blame Iran for their actions.
They didn’t wander into the waters off the coast of Iran. They wandered into the zone around Farsi Island. It sits in the middle of the Persian Gulf.