That is a good question, and no one knows for sure. Several hypotheses have been made and you are free to accept the one that suits you.
1. Since the monkey spoons all have a hook on the stem and they hang by that hook, it would "look like a monkey hanging by its tail" (my favorite).
2. Most monkey spoons have a small figural emblem on the high part of the curve. I haven't seen any that look like a monkey (Some later reproductions supposedly had a monkey as a word play on the name but I have never seen one), however, there is one style that is very hard to figure out. Some people see a "monkey" in this figure (I don't).
3. When people drink too much they often act strangely. In Dutch the term "zuiging the monkey" is an archaic reference to drunkeness.
4. In the language of the sea, a ship which contained the full allotment of grog (rum or beer) was called a moncorn (some people think that the word monkey was derived from this word). Another sailor phrase was 'to suck the monkey' which was used to refer to the practice of drinking alcohol through a straw in a surreptitious fashion.
Take your choice. There is no "wrong" answer.
Another word of caution
Very little is known about these spoons and the only book on silver which discusses these spoons is my book.
I have read every article I could find about these spoons (which is very few) and all of the writers have encountered the same problem with figuring out the purpose and who were the primary purchasers of these intriguing spoons.
I have also exhausted the capabilities of the vast silver book collection at the Huntington Library (Pasadena) in trying to understand these spoons.
Many of the spoons contain silver marks. In almost all cases, the marks appear to be pseudo marks and have not been traced to a manufacturer.
Click these links to see some wonderful pictures of these very intriguing and unusual spoons.1. Very large monkey spoons
In "Two hoof spoons
September 1, 1978 | By ALBERT SCHER; from The Magazine ANTIQUES, September 1978."
" For example, Dutch godparents gave a gebortelepel, or birth spoon, to a newborn child; newlyweds were often given a silver spoon; and an engraved silver spoon was commonly presented to each pallbearer at a funeral."
From the Oxford English Dictionary we have this definition
Pronunciation: Brit. /ˈmʌŋkɪ spuːn/ ,
U.S. /ˈməŋki ˌspun/
Etymology: < monkey n. + spoon n.... (Show More)
A type of decorative silver ladle made to commemorate a wedding, christening, or funeral among people of Dutch origin living in the Hudson River area of the United States. Cf. Apostle spoon n.
Such spoons usually had a hooked stem with a front boss, and a relief image on the surface of the bowl appropriate to the occasion being celebrated.
1833 T. Sedgwick Mem. Life W. Livingston ii. 64 To each of the eight bearers [at a funeral in New York, 1749],..a monkey spoon was given. [Note] This spoon differed from the common one in having a circular and very shallow bowl, and took its name from the figure of an ape or monkey, which was carved in solido at the extremity of the handle.
1881 Harper's Mag. Mar. 530/1 Each of the eight bearers [at a 1749 funeral] was given a pair of gloves, a monkey-spoon, and a mourning ring.
1895 E. C. Brewer Dict. Phrase & Fable (rev. ed.) 852/2 Monkey spoons, spoons at one time given in Holland at marriages, christenings, and funerals. They may still be picked up occasionally at curiosity shops.
2002 www.geocities.com 18 Jan. (O.E.D. Archive) , This monkey spoon has a medallion for a boss. I have never before seen this on a monkey spoon.
Toward a More Perfect Union: Virtue and the Formation of American
By Ann Fairfax Withington, 1991
"People of different denominations had slightly different funeral customs. Members of the Dutch Reformed Church, like other colonists, gave away gloves and scarves, but they also gave bottles of wine, monkey spoons, and doed-koecks (dead cakes), and they were less likely to give away mourning rings."
"Monkey spoon --a spoon with the image on an Apostle on the handle, common funeral gifts"