Why major warship refits are normal lifecycle planning

Are major ship refits usually evidence that something failed?

No; they are a normal, planned consequence of keeping a ship relevant through a service life of several decades.

A major refit does not by itself reveal an organizational, financial, or doctrinal failure. No design can remain technologically current throughout a multi-decade career without new sensors, weapons, machinery, and communications. Navies therefore plan for periodic intervention from the start. The physical growth of modern warships partly reflects the need to reserve volume and capacity for later additions. This watch point connects lifecycle cost, upgrade margin, and initial ship size.