One possible explanation for this is incredibly mundane: It might describe abundant trade goods from what is today the coast of Lebanon.

When the Israelites came to the southern Levant in the 13th century BCE, they found an already thriving civilization there: Canaan. While the people of the region never formed an empire of their own, they did share a common culture and viewed each other as (at least culturally) related. Since they sat at the crossroads of many great empires, like Assyria, Egypt, the Hittites and Mittani, they were also frequently subjugated or at least tributaries to these foreign powers.

The phoenician coast (modern day Lebanon) was somewhat more insulated from this due to mountains to the east and deserts in the north and south. They were also capable shipbuilders, prolific traders and founded many cities around the Mediterranean, most prominently Carthage, but as far as Mogador in modern day Morocco. This made them rich and able to defend themself (or at least negotiate good terms for vassalage), but to even start trading they had to have something to offer and this is where milk any honey come in.

While the phoenician coast was fairly fertile, there simply wasn't enough land to cultivate to support bustling cities (plural, they certainly could have sustained a big city). Lifestock however can be grazed on much less fertile soil and so they kept sheep in the highlands (for wool and milk) and developed fairly advanced beekeeping techniques in lands which could support these uses but didn't have high agricultural yield. This led to a surplus of goods, which could be traded away. Especially after the region had accumulated some wealth, they could afford to import more desired foods (from Egypt for example, but also from Crete or Cyprus) and export even more of their staple goods, which were certainly available elsewhere, but not in the same quantities.

Honey is also a preservant and sterile, which is great for traders and might have led to the appearance, that these people must be literally bathing in honey at home, if they can afford used it for these weird applications instead of eating it.

Thus "the land where milk and honey flows" became synonymous for the phoenician coast, which was somewhat safe from external influences, which is a feature of supreme importance for a people like the Israelites, who had their share of experiences with being enslaved and displaced. They weren't some extremely desirable luxury goods, but where used to describe a region which was wealthy and also comparatively safe for Israelites to be in. This got passed down to the Hebrews and later to Christians and Muslims, as a saying for a "promised land", divorced of its original meaning.

My main source for this is "Auf den Spuren versunkener Reiche" (original title: "Historia de la Humanidad").

I will add to a historical overview from /u/Paladin8 a more literary and broadly cultural undertone, which taken together might even be satisfatory, and give an advice to u/p00rqualitycontent that you might want to repost this to /r/AcademicBiblical, for a more specific ANE relation.

A general point can be made that honey, and consequently bees, have quite a special and privileged role in plenty of ancient cultures and religions, like Egyptian, Greek, Hindu, Ancient near eastern setting generally, and later in Roman culture. Further clarification is needed that in considerable amount of these occurrences, honey is not meant as bee´s honey per se, but rather an extract or syrup ( nectar ) from dates, figs, carob and grapes.

Further, there are similar attestations predating the Old Testament with the usage of similar phrases in relation to fertility in broad Mesopotamian milieu, probably the most pertinent example being Ugaritic myths and Baal specifically, which was an important source for accounts in Genesis.

The heavens rain oil,
The wadis flow with honey. ( KTU 1.6 III 12-13 )

Similarly, in The Story of Sinuhe, around 19. century BC:

... Figs were in it and grapes. It had more wine than water. Abundant was its honey, plentiful its oil. All kind of fruit were in the trees. Barley was there and emmer, and no end of cattle of all kinds. ( Lichtheim, Ancient Egyptian Literature I, p. 226 )

Principally, milk and honey should not be thought about as chiefly nutritious or primarily for gastronomical liking, but through a broader typological and vegetational relation to the promised land as geographically and culturally existent, which is flowing with milk and honey, contrasted to otherwise barren areas and Egyptian lands.

For the land that you are about to enter and possess is not like the land of Egypt from which you have come. There the grain you sowed had to be watered by your own labors, like a vegetable garden; but the land you are about to cross into and possess, a land of hills and valleys, soaks up its water from the rains of heaven. It is a land which the LORD your God looks after, on which the LORD your God always keeps His eye, from year 's beginning to year's end.

If, then, you obey the commandments that I enjoin upon you this day, loving the LORD your God and serving Him with all your heart and soul, I will grant the rain for your land in season, the early rain and the late. You shall gather in your new grain and wine and oil I will also provide grass in the fields for your cattle-and thus you shall eat your fill. Take care not to be lured away to serve other gods and bow to them. For the LORD's anger will flare up against you, and He will shut up the skies so that there will be no rain and the ground will not yield its produce; and you will soon perish from the good land that the LORD is assigning to you. ( Jewish Study Bible, Deuteronomy 11:10-17 )

1.The Origin and Significance of "The Land Flowing with Milk and Honey", Philip D. Stern, Vetus Testamentum Vol. 42, Fasc. 4 (Oct., 1992)

2.The Symbolism of Honey and Milk, Etan Levine, A Review of General Semantics Vol. 41, No. 1 (Spring 1984)