According to the sage that is the Great GW, Brown Malt would have been the only sort available until circa 1800 when the industrial revolution came to the brewing industry. At around that time, it would become far more practical to turn Barley into Pale Malts.
Despite this, darker beers such as Porter and Stouts would remain popular for many years,
Due to the resurgence of homebrewing, I feel that I am not alone in my occasional preference for a strong-ish, malty, dark beer which is definitely enhanced by a Brown Malt addition.