Garden variety Starlink requires a big, expensive, high-powered phased-array antenna, and there are lots of low-power/IoT-type applications served by Iridium for which Starlink is not suitable. Once the Starlink direct-to-cell technology matures, presumably that'll serve those usecases, but it still seems pretty nascent.

Iridium still has a monopoly on high latitudes, too, AFAIK. Their USP is being the only network that works literally anywhere on the surface of the earth.

Under SOLAS, GMDSS equipment is mandatory on ships. Iridium (and Inmarsat) meet that requirement, starlink does not - hence Iridium is still very much around...