As usual I could be wrong (

), but...
I was under the impression that these were the 'proper' straps supplied by Hofner specifically for the 500 series basses.
They 'tied' at the neck end of the body and had a sort of 'clip' that would attach to the tailpiece at the butt end.
It could be that the lightweight, hollow design of the bass prohibited a 'screwed on' strap button anywhere else but maybe the neck heel... and doing that would probably throw the neck alignment out of whack anyway!
My first bass was a Rickenbacker...
My best bass is a Rickenbacker...
My last bass may very well be a Rickenbacker