Also, back in the days, all else being equal, 8' lamps had a slight efficiency advantage, because each lamp-end represented a certain amount of cathode loss. So, two ends per 8' instead of two ends per 4' gave a slight edge. In installations like big box stores with thousands of lamps, it also reduced installation and group re-lamp time especially when comparing 8' single pin vs 4' bi-pin since there's no need to twist or align the orientation.
F96T8/59W was a easy replacement that allowed the reuse of housing for F96T12/75W and F96T8/HO 86W was an easy replacement for 8' 110W.
As the age continues to accumulate, the number of legacy T12 fixtures going for a 2nd round of retrofit is rather few.
For a home garage, going with 4x4 instead of 2x8 is a no brainer. In practice, F32T8s don't really fail for 10+ years in residential use if it has a quality ballast. Bringing in just a handful of 8' lamps is a pain. Bringing home a replacement of a just a handful of 8' lamps is a pain. Storing 8' lamps is a pain.
The low production volume with declining popularity, the high breakage rate in warehouse/transit, difficulty in handling all contribute to higher prices for 8' lamps.
