Because the problem that caused it not to work was fixed, but people on older versions prior to the fix don’t benefit from it. Previously the MSI file was responsible for adding the schedule task which had some issues, now ampinstmgr is repsonsible for it and the MSI invokes that to set up the schedule.
Previous users should be able to run ampinstmgr SetupScheduledTasks in an admin command prompt and have it work.