Why Victorian Britain relied on liners for amphibious transport

Could the Victorian Royal Navy have built a dedicated marine landing ship?

Yes in a limited transport-and-boat-handling form, but requisitioned liners were usually the cheaper practical solution.

A modern dock landing ship would be unlikely in the period, but a purpose-built transport with powerful winches and rapid boat handling was feasible. The decisive obstacle was economic rather than purely technical. Civilian liners already possessed much of the useful handling equipment and could be taken up from trade during a crisis. This made permanent specialist amphibious tonnage harder to justify in peacetime budgets.