I would imagine that bulk rolls are one of the lowest-demand products made by any film manufacturer. I would not be surprised if they are phased out, even with a popular film like T-Max.
When I made a "research" on how convenient would be bulk loading I found a very mixed situation. It's as if some producers did not care at all about it, the roll costs almost as much as buying "bricks" of film.
On the other hand, some other producers seem to bet on it. As an example, in the colour sector where nobody seems to sell bulk rolls, Rollei distributes bulk rolls of both CR 200 (colour slide) and CN 200 (colour negative) that seem to be quite cheap if compared to the factory-made rolls. I suppose this is because small firms like Rollei (Rollei is just the brand, I know that) mainly rely on the "advanced-amateur" market which very naturally leans toward bulk loading if there is a reward.
I also suppose that distribution (intermediaries and final retailer) eat a big part of the retail price. By selling bulk rolls through a "shorter" distributive chain the film makers probably profit more.
The distributive chain of niche producers is short in any case (think Foma, Rollei, etc. on the one hand, and big firms like Kodak and Fuji which are distributed by anybody) and so it makes sense to distribute in bulk rolls.
So I might be wrong but I think it is a matter of distributive structure. Small firms manage to remain competitive, notwithstanding higher per-unit costs - less economies of scale - by using a shorter distributor chain and by "leveraging" it with bulk rolls.
Fabrizio