Clamp crimped. Chromed rail has compromised steel. The corrosion depicted along with the crimping caused a stress riser. In time, the inevitable happens.

The coated Brooks rails will look crummy in time but doesn't have the compromised steel that chrome causes.

Brooks also offered for the Swallow (and other models) a titanium railed frame that won't corrode, but they stopped production for that particular model. It too has limits for rider weight.