If non-traceable costs are not allocated to the various operating units within an organization, who ends up paying these costs?

You mean this is homework? I've seen this question asked, verbatim, of how you just asked it. That would be a pretty weird coincidence if several people are just asking the same question the same way as each other.

The error of this question is assuming that costs that are allocated to an operating unit are paid by that operating unit. Which is a falsehood to begin with. If I run a company with several departments and decide to allocate the cost of my janitor to the different departments based on square footage, the company itself is paying the janitor, not the departments. If I don't decide to allocate it, then the company is still paying the janitor's salary.