The game is funded, they don't need to recoup any costs, any copy sold is pure profit, so why abandon a still valid avenue of reaching customers? Games that are far more niche and expect to sell far more copies still sell retail.
They're making the boxes anyway, it's always cheaper to make them in bulk.
And I doubt it would be hard to find a publisher, given that it's the most funded game on KS, and therefore a fair amount of free publicity on it already exists.