This is not at all a stupid question! In fact, scholars have a couple theories on this. According to the standard interpretation, the cedar forests refer to the famous cedar forests of Lebanon and Syria, which were highly sought after by kings as far back as Sargon. Sargon of Akkad, based in Akkad in now northern Iraq, would boast of his conquests of the far reaches of Mesopotamia, including the cedar forests:
He made them cross the Amanus; he made his troops cross the Amanus. He reached the cedar forest. Amidst its din(?) he bowed down and readied his weapons. He offered a sacrifice, made obeisance, spoke distinctly.
("Sargon in Foreign Lands," vv. 11'-14')
There were not many forests with in either Mesopotamia or Egypt with the quality of wood you could find in Syria and the Levant, so timber from the region was extremely important. The acquisition of a source of cheap timber would most certainly be connected with issues of imperial expansion, and it's no surprise that both Pharaonic Egypt and Mesopotamia as early as Sargon of Akkad both desired control over the region. (warning: PDF)
This particular text comes from an epic of Sargon, although the fragmentary nature of it makes it difficult to know the full extent of the composition. What we do know is that there are many parallels with the Gilgamesh story.
The Sargonid dynasty (ca. 2300-2150) was the first real empire (now often called the Akkadian empire), and Sargon and his descendants' rule, though they were of a Semitic-speaking people (usually called Assyrian or Babylonian based off the primacy of those two cities in latter times), included all of Sumer, a different people with a different language. After its collapse, the city of Ur took over the empire (although lacked its far reaches), which is now known as the Ur III dynasty. Ur was not a Semitic city, but a Sumerian one, and so naturally there was some tension in recognizing Sargon's deeds.
One of the results of this tension appears to be the ascription of deeds of Sargon to Gilgamesh. Since Sargon went to Dilmun, Gilgamesh went to Dilmun; since Sargon conquered the area containing cedar forests, so too did Gilgamesh go to the Cedar Forest and defeat Humbaba.
The precise relationship between the two is hypothetical. One hypothesis is that the journey to Cedar Forests was only created in the Ur III period. The epic would act as a counter of sorts to the Akkadian propaganda that preceded it.
An alternative, one favored by Tigay (p. 78), is that there was always a journey to the Cedar Forest, but only with the Akkadian period did it acquire a precise location corresponding with Sargon's military activity.
Hansman 1976. "Gilgamesh, Humbaba and the Land of the Erin-Trees." Iraq 38.1: 23–35.
Horowitz 1988. Mesopotamian Cosmic Geography. Eisenbrauns.
Kramer 1963. The Sumerians: Their History, Culture and Character. The University of Chicago Press.
Kuniholm 1997. "Wood," in The Oxford Encyclopedia of Archaeology in the Near East, Eric M. Meyers, ed. New York: 347–349. [PDF link]
Noegel 2008. "Mesopotamian Epic," in Foley ed. A Companion to Ancient Epic. Blackwell Publishing.
Tigay 1982. The Evolution of the Gilgamesh Epic. University of Pennsylvania Press.
Westenholz 1997. Legends of the Kings of Akkade: The Texts. Eisenbrauns.