Why HMS Andromeda needed her 4.5-inch gun

Why would HMS Andromeda have been better off retaining a 4.5-inch gun?

At San Carlos she needed an immediately usable weapon against shore threats and had no practical gun after conversion.

Andromeda led the entry into San Carlos Water with orders to engage any threat she saw, but her conversion had removed the twin 4.5-inch mounting. The crew was therefore reduced to considering whether an Exocet missile could be aimed manually at a land target, a poor substitute for retained gunfire capability.