Why Japanese radar inventions did not become fleet-wide capability

Why did Japan take so long to deploy radar after developing cavity-magnetron technology soon after Britain?

Because invention was only the first step; Japan lacked the industrial infrastructure to manufacture and deploy the technology at Allied scale.

Production capacity was the decisive bottleneck. Japan could generate strong ideas, but building reliable systems in quantity and deploying them through the fleet required infrastructure it did not possess on the same scale as Britain. Once the United States joined the Allied war effort, that manufacturing disparity became still larger.