The game would not be able to support the number of projectiles required to make volcanoes dangerous if it was truly random, so it relies on fewer random rocks in all directions and some that are targeted with a larger deviation that can make them miss your ship rather than hit every time. If your ship is moving and turning, you're probably not going to get hit all that much but if it's stationary the deviation is probably not enough to avoid getting smoked 2-3 times.
I think if they reduced the range of the volcanoes it would do a lot to make the area more usable. The current range they have basically forces you to evacuate completely to keep your ship from sinking, which leads to downtime waiting for the eruption to stop if you had to do something specific on that island. If the rocks had less range, your ship wouldn't have to go so far away and you could maybe row or cannon over to the island to try to continue doing your quest in the middle of the eruption (which is more fun than waiting) and your ship would still be at risk from pirates because it's a healthy swim or row away to get back to it.