IBM wants Linux to succeed. They probably don't want to dedicate the resources necessary to be sure that OS/2 is absolutely clean before releasing what they can. (AFAIK, Micrografx still has rights to a lot of Presentation Manager, e.g.) Plus, the people who really know OS/2 left long ago. :-( So, doing anything to distract from their Linux push would probably be regarded as money down the drain and counterproductive.
But it would be very nice if they would release things like the design documents for the Workplace Shell so that it would be easier to port to Linux by those who have the interest and the skill...