The cost of for example OATs modular ground school is I think at most about a grand less than their residential ground school. I would imagine that OAT do not make a loss on their residential ground school. Therefore the difference in costs between the two types of theory training does not account for the difference in cost between integrated and modular courses.
Given that integrated and modular courses involve roughly the same numbers of dual and solo hours, it would be perfectly possible to put together an integrated course for the same price as a "structured modular" course, so why doesn't someone do so?
I for one believe that the integrated route is better for getting the ATPL, as it involves less hoops, however the reason im not doing it is because the extra 30grand or so is not justifiable. If someone put on an integrated course for say 35k, which i think IS perfectly possible they would be overwhelmed with interest.