The reasons are simple-ish...
-- Less Weight.
-- Less heat.
-- A10 = M6 on track (roughly)
-- more control, road course drivers like that
-- 1LE, #racecar, etc chest-thumping
And yes, the Z/28 was manual only. The 1LE models are all manual only. The Viper ACR was manual only, GT350R manual only...it's pretty typical to see a dedicated track car offered in manual transmission only.
The few exceptions are very expensive, and very exotic. (eg. Porsche 911 GT3, McLaren, Ferrari)
You can be pretty well-assured that if they didn't include something as standard, then it didn't make the car faster. And if something didn't make the car faster...then it's not an option worth offering on this car.
