The 2nd generation Mustang is the more unpopular Mustang of the six generations. The 2nd generation Mustang was offered in the mid-late 1970’s and early 1980's. Until 2015 this was the first and last generation Mustang to contain a turbocharged 4 cylinder engine to comply with government emission regulations.
It's not that people think that this generation is ugly, but it was difficult to purchase a sports car that was slow and in some opinoins not as good looking. In recent years they have picked up more momentum within the car culture, but nothing compared to the original before it, and the Fox body’s afterward.