By default, the error log list is deleted once in every 180 days. But you can increase the cleanup frequency to accelerate the backup process.
Example: If you want to cleanup the Error Log list every 30 days, then use the query,
update GlobalConfig set PARAMVALUE=30 where CATEGORY=’CLEANUP_TASK’ and PARAMETER=’CLEANUP_ERROR_LOG_LIMIT’;
The maximum limit for cleaning up error log list is 365. If you want to disable the cleanup, then set the parameter value to -1.