Not always the manufacturer's decision. In the UK, owners can report possible safety issues to DVSA, and if there are a sufficient number of reports for the same issue, DVSA will investigate with the manufacturer. Depending what the findings are, DVSA may require recall action to be undertaken.
Also DVSA used to give manufacturers time to obtain sufficient stocks of parts for the recall, before announcing the recall.
That is no longer the case. If a recall is required, it is announced regardless of whether the manufacturer has the required parts or not. This is why sometimes recalls now take longer to complete.