As indicated by others, the autobahn was started prior to WW II. It was
designed around the concept that the fastest speed on it would be
around 100mph (pretty close to top speed on most cars manufactured
prior to WW II). While there are some sections that are straight, it
has more curves than US interstates (and is less fatiguing to the
driver because of this.)

It was also built to a higher standard than US interstates (thicker
roadbed) and hence needs less maintenance than US Interstate highways.