Sure many reasons.
1: Not befitting the nature of a GT car, a cars aesthetics is really important to me, but lowering. it's just wrong on a GT IMHO.
2: Looks IMHO ridiculous, particularly with the wheel not sitting in the centre of the wheel arch.
3: Shorter springs means harder springs, which does translate to increased NVH (Noise, Vibration, and Harshness) (Noise Vibration Harshness) in the ride.
4: Messes with the suspension geometry, requiring work to get wheels aligned correctly, but depending on how low you go, really may require replacement of other parts such as control arms to get the suspension geometry correct.
5: Given the state of roads in Australia and the fact the Stinger is quite low as it is, there is a risk of suspension bottom out on hard cornering (really don't want this) it could cause loss of control.
6: Increased tyre wear if not thought through properly and wheel aligned correctly.
7: In "spirited driving" Tyres rubbing on wheel arches, never a good experience.
8: Will put extra load and forces on suspension components, and has a material impact to your warranty, this is a huge grey area that the dealer could get away with if for example there was excessive wear on lower or upper control arm bushings, ball joints, or even something as simple as tie rod ends.
9: Generally it will decrease the handling dynamics of the car and as such will mean the car will not handle as well as it would at the original suspension height.
10: Again depending on how low you go, may increase rear drive shaft wear particularly CV joint wear.
I'm a purist, a GT car is comfortable, refined, sporty, performance oriented, but not a hard edged sports car. A GT car should get you and passengers from A to B in refined comfort but also offer the performance and opportunity to enjoy those roads that scream out "Drive Me". You should be able to get out of a GT car after 8 or 10 hours of driving and feel like you just got off your favorite arm chair.
I get it, I understand why people mod cars and I get why people like to look of a lowered car, but boy it will come at a large cost of IMHO reduced enjoyment of the machine.
Cheers Hemz