Racing scows are flat because that hull design has a, theoretically, unlimited hull speed. They are great for shallow water with retractable bilge boards, one or two, but they were, and are, a popular sailing design in northern Europe where many of the early Wisconsin settlers originated. Flat hulls are very common in lake or flat water racing worldwide. Sonder boats with fixed fin keels are another good example. There was an active racing fleet on Lake Winnebago starting in the 1860s. They had "A" scows(38 feet) hitting 28+ knots even at that time. The large merchant sailing vessels in the Great Lakes were often narrow, for canals, flat bottomed with large centerboards, unfortunately I don't think a single one survived into modern times. I guess it would be safe to say scows are the most popular sailing hull of all time in America, the Sunfish is essentially a scow hull. Even the wood hulls were beach-able, we just didn't have any, beaches.
Here's a picture of the Oshkosh Yacht Club with some scows, maybe MCs, up on lifts. That could be everybody in the whole city there too.