The author left out a few vital details.
The market for musclecars is huge. People want Style. many of them do not LIKE the style of the mustang and they don't want one. in the 60's GM cars had WAY more style than everyone else. Just look at a 67 GTO, 67-69 camaro/firebird.
The newest mustang opened up people's eyes, but there are still people who don't like the style (so they didn't buy it in hopes someone ELSE will make the musclecar they really wanted).
that's my 2 cents