There are a number of reasons for this—not least, such organisations still believe that their own application needs are different to everybody else's, and given software's ability to help companies differentiate, they may well be right (a similar argument exists for public organisations, which holds rather unique positions in their parent countries). In addition, existing (legacy) systems have not gone away, and they still need enhancement and/or maintenance.
New applications are required to meet new business needs, which require new software development, or a combination of package procurement and customisation. Where software is developed in house, it tends to be focused on the business processes that differentiate the organisation. These are the processes spanning traditional, function-specific application stovepipes, delivering capabilities at the edge of the organisations that touch customers, partners and suppliers.
