If the job fails to schedule its next occurrence then the job never runs again? So for quarterly jobs, you won't find out about the failure for at least 3 months and if it languishes in a broken state for as much as 6 months you could have serious consequences of a skipped job? (or adjust the timings for whatever interval; long or short it's a similar problem)

I would not want to be the person to inherit your role. Upon first-glance inspection at what is immediately visible, the jobs are all set to run once. There also exists some proprietary control tables that don't seem to be used in any business division. Until I dig into the package to discover the self-scheduling feature, it isn't obvious there even IS a schedule.

I guess basically I'm curious why it's better to roll-your-own than to use the native scheduling feature that anyone educated in SQL Server would already understand.