Reusing parts is a very important and common concept.
Using the same DC motor 4 times means you have to deal with only one motor type. If you choose a 2nd type of motor for the roll, you have to fiddle with the characteristics of two motors. Using a motor with more torque usually means that you need a different drive circuit. From here on the problems are proliferating.
- What if the supplier of the bigger motor stops selling the motor?
- What if the driver circuit of the bigger motor does not have the
precision of the smaller ones?
- What's the price to buy 1 + 2 motors vs. buying 4 of the same kind?
If you are a company building industrial robots you buy DC motors in bulk. You use few standard motors that your engineers are familiar with. The driver circuits are proven and tested.
If you face a higher torque requirement, you simply add another familiar motor. It's not economical to pay somebody finding a better suited motor, which has several possible drawbacks as pointed out above.
As a company your goal is to sell robots, not to overengineer them.