Why land rockets do not automatically belong on ordinary warships

Will navies put land-based multiple rocket launchers on warships for cheap shore bombardment?

Usually not, because the launchers consume space better used by versatile VLS weapons, though a specialized amphibious-support ship could justify them.

A large rocket launcher occupies scarce ship volume that could hold a vertical-launch system with longer-ranged, more flexible weapons. Supplying a fleet with a separate rocket type also creates a logistics burden that may not be justified by its lower unit price. The economics work better ashore, where launchers and reloads do not have to displace other naval systems. A purpose-built amphibious bombardment ship might still make the trade, but the answer does not favor adding the weapon to a normal general-purpose combatant.