The same reason you could write part of your site in COBOL (Micro Focus) because you have a large body of legacy and need to get to the web.
It gives you a way to connect your enterprise system to your corporate intranet.
Seems like a pretty stupid way to do it. Why not just use the raw data from the data files or direct access to the DB/2 database? Does this even handle the ebcdic to ascii conversion? Or packed decimal numbers?