Honestly... what did you expect?
I find you get away easy!
What kind of technical answer are you looking for?
Gear ratios can be found online I am sure, or in a workshop manual.
Technical response:
The 1st gear of the Mazda BT-50, or most pickups for that matter, are quite short. Most dont get you past 30kmph at max rev!
This is because the payload of a pickup of this class is in the vicinity of 1000kgs. For the vehicle to comfortably move off from rest with this much load requires a large ratio 1st gear.
The max weight of these vehicles are about 2700-3000kgs. So the payload capacity is about 1/3 of the overall MGW of the vehicle. Unladen, a pickup carries about 65-70% of its carrying capacity.
That is a huge difference between that of a passenger car, whose max capacity is about 1700kg, with a 450-500kg carrying capacity. Meaning that a passenger car (or SUV) is only required to possibly carry 1/5 of its MGW as cargo/passengers. Meaning that is almost always operates at 80-90% capacity.
Given this information. It can be seen that a 1st gear ratio to match a passenger car would almost always show no huge difference while moving off from rest in relation to that of a pickup.
Additionally, there the fact that your talking about a diesel engine and a gasoline - where power delivery and torque are worlds apart. These factors also influence gear ratios.
But I will leave that for someone more learnt about the delivery of torque and power.. like a mechanicl engineer?