Following a bit of research into the Strait of Hormuz I’ve discovered that the shipping lanes deep enough to permit passage of oil supertankers are just 6 miles wide: two miles wide inbound, two miles buffer zone and two miles outbound.
The depth is 60-100m and the draught of a fully laden supertanker around 30m, so it seems that if just a few of the stricken ships (with more to come probably) currently stationary in the shipping lanes were to sink then the entire strait would be rendered too shallow and be closed indefinitely until complex salvage operations could be undertaken.
Iran would, as it were, be shooting itself in its foot by trying to sink ships as it too requires the strait for oil exports but desperate times lead to desperate measures…