You might laugh when looking at it through the optics of today but in the 60's culture of Bigger, Faster, Better the argument held some legitimacy. Problem in execution then as now was the cost of the body work - not cheap in an era of no home mig welders and .023 wire. Lots of big window donor bugs around in the mid to late 60's that had been written off (many went to dune buggies) but why bother when you could buy a big window beetle for about the same cost of the body work done by a pro.
Ovals were simply not that valuable or seen as a desirable ride. Small cars were cheap A to B transportation and not much else. Hot VW's, VW Trends and other mags certainly changed our thinking.
I never saw another beetle with the big window graft.