Whilst you might expect backpacker-style tourists to be nearly broke, (a) many tourists have a great deal more money, and (b) backpackers have parents who would perhaps stump up to get their child out of jail.
And the fear of punishment will encourage compliance.
i still don't think it will control virus transmission. my opinion.
Agree, backpackers are a free spirit. Any tourist that comes here is a threat now as now, there is no point coming here. Given that there is no reason for a tourist to come here it seems an easy fix to block the borders except for Kiwis. As you are not blocking a revenue stream