SQL Server Job History Disappears After 5 Days
That job has to do with policy-based management, not SQL Server Agent jobs in general. In Object Explorer right-click SQL Server Agent and select Properties, then move to the History tab. What does it say here:



You can adjust those settings so that it keeps more rows overall, more rows per job, and keeps history longer. I am guessing either you have a lot of jobs on this server or these settings have been changed.