I would assume that the rebranding of film and the resultant sale at a lower price is like the difference between wholesale and retail sales. And of course volume is important.
I would think that the film manufacturers would love to sell all of their film at retail prices. But if they also sell the film cheaply to someone else (but in a very large volume), they will sell more rolls than they otherwise could. Yes, there's probably less profit per roll but at the end of the day they are selling more than they would have without the wholesale agreement.
Increased volume, lower per unit profit, still means profit overall. And it means more demand.
I'm sure that if the manufacturers were losing money out of the deal, they simply would not do it.
Surely it's also about costs. Selling the base film stock direct to Freestyle without packaging, branding, printing, support etc. would lower the cost.
Anyway, sorry if that's too many words on the subject. Just order some film and enjoy it, like what Steve said