Why adding a slipway does not solve a naval production bottleneck

Why could Japan not solve its naval construction shortage simply by building more slipways?

Because a slipway depends on a much larger industrial system and on scarce stable waterfront land already competing with ports, housing, and commerce.

The visible slipway is only one part of a shipyard. Expansion also requires workshops, transport, cranes, skilled labor, and flat stable ground beside navigable water. Those sites are attractive for cities and commercial ports as well, and Japan had less suitable land than Britain. On the Mersey, Liverpool's commercial port stood opposite Cammell Laird at Birkenhead, allowing urban and shipbuilding functions to occupy separate banks.