I think the idea here is to force them to develop some sort of empathy for what people who work in fast food have to deal with on a day to day basis and learn from it (which should reduce recidivism) as well as some punishment, hence the 30 day jail sentence and 60 days working in the job (or just 90 days in jail).
I’m personally in favour of this. A jail sentence is purely punishment, whereas this feels like a combination of punishment and rehabilitation which is rare but tends to provide better outcomes (this tends to be contentious so I won’t provide links, but please do look it up if you get the chance).
Woman who threw bowl of food at Chipotle worker sentenced to work 2 months in fast food job ( www.cnn.com )
Watch: Billionaire CEO says unemployment 'has to jump' to put 'arrogant' workers in their place ( www.rawstory.com )