Because it has historically been proper etiquette to serve such food to other people with tongs, rather than touching it with one's hands.
Household guides and books of etiquette going back at least as far as the 19th century talk about all of the things properly served at meals with various sorts of serving tongs: cubed sugar, pickles, sandwiches, cake, sardines, asparagus, steak, and so forth.
Toast is served with tongs, too. Note that, whilst metal serving tongs historically exist, because toast is generally made nowadays in an electric toaster, serving tongs for toast are nowadays made from plastic or wood for electrical safety.
toast tongs from Myrtlewood Factory Outlet of Oregon U.S.A.
Ironically, wood would have been entirely unsuitable for the historical way of making buttered toast, which was holding it in front of a fire with a metal toasting fork.
A seventeenth century wrought iron toasting fork from the collection at the Shakespeare Birthplace Trust
M. Kasson (in further reading) goes into a lot of detail of the explosion of specialized flatware in the middle to late 19th century, and touches upon the notion that many of these were over-specialized by silvermongers to expand their sales catalogues.
In practice, as explained in other further reading, using the wrong tongs is not as gauche as one might think. As Mrs Hale demonstrates, in a recipe For Taking Grease out of the Leaves of Books, when one type of tongs is unavailable another sort will do, substituting hairdresser's pinching tongs for fire tongs in this particular case. (It's below a recipe for using toast for removing wax from velvet, interestingly.)
Of course, fire tongs (which are inserted into a fire, notice, rather putting the kibosh on the idea that this is unsanitary) were a regular substitute or indeed primary kitchen utensil for handling food. Emily Post described some of their uses:
A pair of long tongs is useful for arranging coals and for moving anything that is hot. They are ideal for turning corn or potatoes as they cook in the coals and better for turning a steak than a fork, which pierces the meat and allows the juices to escape.
— Emily Price Post and Elizabeth Post (1975). The New Emily Post's Etiquette. Funk & Wagnalls. p.354.
One can find much the same advice continued today in advice to owners of barbecues:
special charcoal tongs can be bought, but a pair of standard metal tongs is sufficient
— Cara Hobday (1995). Barbecues. Shooting Star Press. ISBN 9781573351102. p. 79.
- Paul Bourcier and Ruby Rogers eds. (2010). "Serving utensils". Nomenclature 3.0 for Museum Cataloging. American Association for State and Local History book series. Rowman & Littlefield. ISBN 9780759111936. pp. 148–149.
- U.S. Fire Administration (October 1980). "The kitchen: toast tongs". Teaching Fire Safety Through Exhibits. Federal Emergency Management Agency. FA-36. pp. 27–28.
- "Toast, Buttered". Cassell's dictionary of cookery. London: Cassell, Ltd. 1883. p. 979.
- "Hot Buttered Toast". Cassell's Household Guide. London: Cassell, Ltd. 1869. p. 313.
- William Kidd (1852-02-28). "Buttered Toast". Kidd's Own Journal. volume 1. issue 9. London: William Spooner. p. 132–133.
- Judith Martin (1983). "Table Manners". Miss Manners' Guide for the Turn-of-the-Millennium. Simon and Schuster. ISBN 9780671722289.
- John F. Kasson (1991). "Table Manners and the Control of Appetites". Rudeness and Civility: Manners in Nineteenth-Century Urban America. Farrar, Straus and Giroux. ISBN 9781466806634.
- Sarah Josepha Buell Hale (1857). Mrs. Hale's receipts for the million. Philadelphia: T.B. Peterson. p. 63.
- Alison Ravetz and R. Turkington (2013). The Place of Home: English domestic environments, 1914–2000. Planning, History and Environment Series. Routledge. ISBN 9781135158453.