Why does the music from Cape Verde sound so sad?

Might one reason be recurring famine?:

Despite its name, Cape Verde is an arid landmass with minimal agricultural potential.  The excess mortality associated with its major famines in unparalleled in relative terms.  A famine in 1773-76 is said to have removed 44 percent of the population; a second in 1830-33 is claimed to have killed 42 percent of the population of seventy thousand or so; and a third in 1854-56 to have killed 25 percent.  In 1860 the population was ninety thousand; 40 percent of Cape Verdeans were reported to have died of famine in 1863-67.  Despite a population loss of thirty thousand, the population was put at eighty thousand in 1870.  Twentieth-century famines in Cape Verde were less deadly, but still extreme relative to most contemporaneous ones elsewhere: 15 percent of the population (or twenty thousand) in 1900-1903; 16 percent (twenty-five thousand) in 1920-22; 15 percent (twenty thousand) in 1940-43; and 18 percent (thirty thousand) in 1946-48…

…such death tolls imply extraordinary noncrisis population growth.  For instance, if the population estimates for 1830 and 1860 are credited, making good the damage inflicted by the famine of 1830-33 would have required an annual population growth rate of about 4 percent between 1833 and 1860 — despite the loss of a quarter or so of the population in 1854-56.

That is all from the new and noteworthy Famine: A Short History, by Cormac O Grada.  Here is the book's home page.

Here are the author's working papers on famine.