Why do large navies underinvest in hospital ships?

Why do more large navies not invest in hospital-ship soft power when conversions can be relatively affordable?

Budget priorities limit hospital-ship provision. An NHS-linked medical fleet is proposed as a British example.

The question cites an LPD conversion costing roughly $200 million as an example of relatively affordable hospital-ship provision. Budget priorities can still prevent governments from funding such ships. Britain's public celebration of the NHS prompts a proposal for a naval medical partnership. Hospital ships jointly crewed with NHS personnel could take that healthcare role overseas. In this argument, such a fleet would connect a prominent national institution with sustained medical diplomacy.