No idea. Do you think it was pitched like that before the conflict began?
So, to me, the two possibilities are: the military told the administration it couldn’t control the strait without boots on the ground, and Trump disregarded that advice.
The other possibility is that the military was overconfident. We know it has been developing plans to attack Iran for decades. It’s possible the military thought it could control the strait based on obsolete plans that didn’t account for new developments like Iranian fast boats and drones.