The Mother Earth syndrome.

The "flow" in "flowing with milk and honey" is zavat, whose root is used both for waterways (streams, rivers) and bodily discharges (sexual, usually, both male and female). So the land is "flowing" (in the biblical sense) with basic needs.

Interestingly, bees are unclean, yet we see Yahweh praising the land he has prepared for his chosen people, the same people to whom he will say "bees are unclean," as flowing with honey. We see characters throughout the Tanakh consuming honey, and in the NT, John the Baptist is living off locusts and honey (arguably one of the last fully Jewish characters we meet since he never sits under Jesus's teaching).

Why are honey and milk chosen to represent the basic needs? If a land is fertile enough in grass and flowers to support cattle and bees, it is a good land for humans too. We know that the ancient Semitic cultures viewed honey as divine and used it as sweetener. For example, pharaohs are found buried with jars of honey still unspoiled today. Milk is, of course, the natural indicator of life since newborns require it to live.

Some speculation: I read an article back in college that the Song of Solomon draws heavily on non-Jewish mythology involving Ishtar, specifically citing the "milk and honey" description for the wife as a connection to pre-Jewish mythology tied to Canaan (since, you know, bees are unclean but honey is considered good). I find this suspect, but it seems plausible enough considering how "worldly" and "corrupt" Solomon became. I can't find the article I read right now, but hopefully someone else can speak to its veracity.

FWIW, the Ugaritic text KTU 1.6 III 1-13 (the Baal Cycle) speaks of the heavens raining oil and the wadis running with honey (šmm.šmn.tmṭrn / nḫlm.tlk.nbtm).

In the Akkadian CT 39:13 (an omen text), "The soil of Nippur oozes honey (dishpa)," and "the soil of the land exudes . . . milk, honey, naphtha, upati."

Also: a Sumerian hymn to Enlil, translated by Kramer, has the line "Of the festivals overflowing with rich fat (and) milk"; but a more recent translation of the same text by Black et al. reads "At the festivals, there is plenty of fat and cream." I don't know anything about Sumerian, though.

Or is it possibly a mistranslation?

Interestingly, there was a fairly recent article in a major Biblical studies journal that argued that the word "milk" (ḥlb) in "milk and honey" is actually to be understood as ḥēleb (fat), not ḥālāb (milk). Not sure how convincing I found it, though. (Cf. also Heckl, "Ḥelæb oder ḥālāb?"; Guillaume, "Thou Shalt not Curdle Milk with Rennet" and 'Binding "Sucks": A Response to Stefan Schorch')

That land was good for raising goats (milk) and was home to a certain type of bush that attracted bees to build combs in, producing honey.

Source: Dr. Jack Sasson

Edit: Worth checking out Michael Coogan's introduction to Hebrew Scriptures. He loves talking about the Promised Land.