Simplify the following text for a Grade 12 native English-speaking person.
Original: 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 .
Simplified: 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 .