Thats because its a low cost model, the 4 speed auto does the job and it keeps the weight down.I dont understand that it only has 4 automatic, today 2018/2019 it should be like 8 or 9 or similar and they gas milage would be much better and the accelaration. In 2002 Jeep Wrangler TJ had 4 automatic. The new Jeep Wrangler JL has a 8 speed automatic
I also don't see the need for a 7-8 speed auto in this type of small 4x4 with a 1.5 litre NA motor.
It's a proven transmission, the only thing i did to my Gen 3 Jimny was to add a transmission cooler to the 4 speed Auto, for towing up mountains.
Is it the best auto, nope, but i have faith in it off road