The government couldn't foresee all the food we would have nowadays and nobody would need to poach.
This isn't a very sound argument: "we" have a lot of food nowadays, but it doesn't necessarily reach the people who need it. Poverty and hunger have increased in the US over the past few years. Over 15% of rural households are "food insecure"
(the current euphemism for not having enough to eat). Not that they're all out there poaching, but that motivation is still there for many people.
I'd also question whether poachers worry too much about the niceties of the NFA, but that's another discussion entirely.