I think you have it, especially with the first, but also I couldn't find very much coastline for Polisario-controlled territory here https://en.wikipedia.org/wiki/Western_Sahara#/media/File:Wes...

And of course there's the background indirect issue where the world's largest navy is stationed half on the same ocean.

Piracy used to be common in North Africa, but more along the Mediterranean Coast where there is far more shipping. The Red Sea is also a choke point.

One theory is that the shipping lanes there are not forced to go near the coast.

Another is that Somalis are extra prone to piracy.