While there may be 145 000 power supplies potentially affected by the defect, there can be far many more than 145 000 Chromebooks in the wild.
The adapters that got recalled are likely from a single batch or a batch that contains a particular component that came from a bad batch and only the adapter batches affected by the defect are getting recalled.
This is why batch numbers, manufacture date, serial number or some other methods of tracing devices back to their manufacturing batch or component batches is necessary - limit recalls to the narrowest scope possible.