A lot more than the grille, taillights and 8.25 changed. Fenders are different, hood is different, entire interior changed (lots of plastic), front bumpers were redesigned, front valance went away. And the dreaded "beak" showed up. Plus some of the changes from '72 weren't great either, no rallye gauges, power was down, goofy plastic side markers. And the twin scoops went away! I think most of it though is that a lot of folks just prefer the earlier body design.
Some good things happened too, all the V8 cars got disk brakes and the BBP. Large upper ball joints started, the spool mount K frame, redesigned front sway bar, and the fold down seat. And if you like the snorkel scoop that showed up.
And on top of all that they sold more cars 73+, highest year of production for the Dusters was '74. '73 Dart sports actually outsold the '72 Demons, and were almost on par with the '71s for total sales.
1971 Demon
Fastback Coupe: 69,861
340 Fastback Coupe: 10,098
Total 1971 Demons: 79,959
1972 Demon
Fastback Coupe: 39,880
U.S 340 Fastback Coupe: 8,700
Total 1972 Demons: 48,580