Why the County class used its distinctive missile launcher

Why did the Royal Navy adopt that launcher on the County-class guided-missile destroyers?

Because it was the available British-built launcher, and its simple elevated arrangement worked.

The answer reduces an unusual-looking installation to procurement reality: it was the launcher Britain had available. Its elevated box structure was mechanically simple and domestically produced. That combination mattered more than elegance when the Royal Navy needed a practical guided-missile installation. The moment is a concise example of how available national technology constrains warship architecture.