Most boats are gel coat to a degree. But the trailers (especially for saltwater boats) are fully aluminum. Those need lots of care lest they oxidize to nothing after a few years. And of course, tuna towers, cobia towers, etc are typically anodized aluminum and they need love too.
Lots of people do wipe them down with WD-40, but that can create a residue elsewhere on the fishing tackle that is often frowned upon. Lots of ways to skin a cat…