With the US blockade on Iranian shipping and ports in force along the whole of the southern Iranian coastline, and the railway link to China through the border crossing point with Turkmenistan at Inche-Buren damaged, the route across the Caspian has become the only cargo route for heavy traffic which remains under Iranian sovereign control.
When Iran began supplying drones to Russia a few years ago, they got involved in Ukraine’s war, on Russia’s side. This is just them suffering the consequences of that.
Also, you seem to think Iran’s position is much stronger than it really is. They’ve got their hands full with their current range of foes, they have no need to find more. They’ll make some noises and threats, then do absolutely nothing at all.