Original: Due to the slowly dwindling supply of suitable donor cars, Baja Bugs have been greatly supplanted in recent years by tube-framed, purpose-built buggies known as sand rails.
Simplified: Though few Baja Bugs are built anymore since the creation of tube-framed, purpose-built buggies known as sand rails and the shrinking supply of early Volkswagens, they remain a popular choice in the desert since few beaches in the US are open to for use by cars or motorcycles.