I don't know the true answer to the "why sell oversize" question, but it may be a reluctant response to customer demand. I can't think of any modern engine manufacturer who likes or supports reboring, because results are usually a long, long way short of factory quality standards. However sometimes their official spare parts service peddles the components because there is a dollar in it and their unaffiliated competitors are doing it.
Usually the repair manual is prepared by technical people under the influence of the engineering department, while the spare parts list is prepared by the commercial people in the spare parts department.
