Mostly because you don't seem to be doing a good job of enforcing the terms you set and now you're punishing him for not taking them as seriously as you'd like when you haven't really given him the impression that you were serious about it. You say he blew off an interview to go camping, but you let him go camping. You could have said no and taught him that responsibilities sometimes take priority over fun.
Also, INFO: You say you live in a rural area with no public transportation and he can't drive yet. Are there even any/many job options within walking/cycling distance that could get to since he can't drive yet?
I don't know how the driving thing works in the US, is it 100 hours driving in general? 100 with a driving instructor? If it's the latter, does he have to pay for the lessons himself? If it's just 100 hours in general, have you and your husband been making the effort to take him out for lessons (maybe letting him drive on the way to the supermarket or school)?