If illegals who were released and told to report to a hearing on date x, and they didn't show up, what makes anyone think that if they take part in a work program and the end date arrives, that they'll show up (for a bus ride home)?
The constantly unanswered question is, "Why should any of these interlopers bother to jump through hoops for citizenship, or other legal status, when they have everything they want with the current status quo?"
We have had a guest worker program before- the bracero program. It worked. Workers went back. That is because the employers who bring them in are financially responsible that they go back.
The weak point in any of these programs is, that the illegals will not believe that this country will have the will to send them home EVER.