Rm, it must be that population pressure from a successful HG culture pushes people into agriculture since all successful (ie those that survived) cultures made the transition or assimilated (either from above or from outside) into them.
Walking through the reconstructed Mississippian city at Cahokia probably gives you a very good indication of what the early tells in SW Turkey and along the Tigris and Euphrates were like. The question is why did the Mississippian towns come along 6000 years after the Mesopotamian settlements.
Homo sapiens sapiens HG people were living in Anatolia and Mesopotamia for at least 30,000 years. The slow accumulation of culture, the population growth due to their successful and (here I speculate) the stability and comparative peacefulness of these original Mediterranean people pushed them into settled village life starting around 7000 BC.
In the Americas, the pressures to form villages and an agricultural way of life apparently did not come until the first millenium BC and in North America, probably not until 700 AD (the earlier Adena/Hopewell cultures were not or were only minorly agricultural). Was this because they had a continent full of game, fish, fruits and berries? Probably, as rmariamp points out, it is an easy life style.
There is another point, however. There seems to be a need for a seeding culture, one who starts out and (dare I say it) diffuses ideas to its neighbors. In Mesopotamia, this was the Sumerians. They were intrusive into the area (some say from the south) and started the civilization ball rolling. The Mohenjo-Daro and Egyptians were influenced if not inspired (or diffused) by them. Even after the highland barbarians from the north and east started causing havoc in to Mesopotamia, there was always a civilized group that survived or a war lord that encouraged the arts of civilization so the area never lapsed into complete barbarism. (The continuing presence of Egypt might have helped too.)
The earliest sedentary although probably not agricultural culture that I know of in the Americas is the Poverty Point people of Louisiana, 2000-3000 BC but that keeeps getting pushed back. Their civilization was destroyed/atrophied/abandoned and nothing took its place. The Adena people (~300 BC) and their neighbors, the Hopewell (0 AD), put on a good show and probably were on the edge of agriculture when they collapsed (possibly due to the invasion of the proto Cherokee/Iroquois). There was no followup continuity. The Mississippians (800 AD) were undoubtedly influenced by Meso-America, had a thriving agricultural society (apparently they were a little short on protein though). Some currently unknown factor knocked them down (in the north, it was probably invasion from the Algonquian speaking peoples). And unfortunately, that was the last chance.
In meso America, there was an interesting seed culture, that of Teotihuacan. It cross fertilized if not inspired the Mayan civilization. While it was destroyed (~600AD), Nahuatl warlords maintained the conquered civilization’s trappings and formed the Toltec culture, similar to what had occured in Mesopotamia 2000 years earlier. This, too, fell to later Nahuatl invaders and, after a dark age, later peoples, the most famous of which were the Aztecs, took up the civilization torch. But the clock had run out.
So, my guess is that the American Indians got a late start compared to the Mesopotamians because America’s HG resources were not anywhere near exploited and, once agricultural civilizations were started, there was not enough continuity after invasions and dark ages. Luck had a lot to do with it.