In simplistic and generalised terms...
Many developing countries have their development restricted because a large proportion of the country works in factories making stuff for developed countries. If you take away the factories there are two pathways for the future:
1 - "Go back to hand-to-mouth subsistence farming" (although that misses the detail of what many countries were like before Western imperialism)
2 - you free up a workforce who can get better jobs, and/or grow a domestic manufacturing industry where the profits remain in the domestic economy, rather than profit being sucked out by transnational corporations.
In the short term the latter pathway is not desirable for us in the developed world as stuff becomes more expensive to make, and a new set of competitors are created. Underdevelopment is useful if you want cheap stuff and want to remain part of the dominant economic order. Having Indians working in call centres is much better for the West's knowledge economy because people aren't using their degrees for creative or entrepreneurial ends, or the public good.
