"People have to be able to support themselves and their families; if they know that there is very little awaiting them on the other end, that has to be a disincentive," Brunson McKinley, IOM director-general, said.
McKinley, who ended a six-day mission to Sudan on Saturday, also visited the war-ravaged western region of Darfur and Juba, the capital of South Sudan.
"When you look at Juba and I guess the country beyond Juba which is even poorer, you see a lot of work needs to be done," he added.
A January 2005 peace deal ended more than two decades of war between the Sudanese government and southern rebels. The war, Africa's longest-running conflict, displaced about four million people - nearly half of whom ended up in camps on the edges of the capital, Khartoum.
In addition, much of the land is still not available for farming and grazing livestock because of landmines and other unexploded ordnance. The Ugandan rebel Lord's Resistance Army also poses a security problem in Southern Sudan, particularly in Equatoria region.
"When you play that back into the experience of the displaced persons or the refugees, you have to say that it is really the ones who are the most courageous who are going back now," McKinley said. "And you can understand why others are waiting until things get a little bit better."
IOM has helped more than110,000 southerners return home from camps around Khartoum since 2005. During his visit, McKinley saw off about 500 displaced persons returning by barge to the south.
The barge is being used because the onset of the rainy season has made travel to the south by road almost impossible. This year, IOM hopes to help more than 60,000 displaced southerners return home.
However, the majority, especially those who have established themselves in the north, are staying put, fearing the prospect of starting from scratch.
"I am sure that there are some people living in camps for displaced persons who have not been able to find employment, who have problems, who are unhappy where they are, who live out of a kind of desperation," McKinley noted. "But others, certainly [want to] go back because they believe or at least hope that things will be better and that they can contribute to rebuilding their home villages, their tribes and their regions."
Under the north-south peace deal, the south gets 50 percent of oil revenues from wells in the south. Donors also pledged US$4.5 billion, some of it earmarked for rebuilding devastated infrastructure and creating a peace dividend. But the government of South Sudan says it has yet to see the bulk of the pledges.
As a result, infrastructure is still largely undeveloped in the south, according to aid workers in the vast region.
"Most people want to go home. They are homesick; they are nostalgic for their home place, their home people, and their environment," McKinley explained. "I think that as the south develops, gradually people will say 'alright, now it is good enough, I'll go back and help to build it'."