Accurate signal reconstruction
sin(x)/x or sinc is the function of the ideal low pass filter.

Your scope has a sharp cutoff at f/2 (at least you are prentending that), and using the ideal low pass filter for interpolation then gives you a result better matching the characteristics of that ideal scope than linear interpolation.

Or in short: with sinc, you at least don't see such artifacts as straight lines where there should be distortion.