I don't want to answer for the devs, but generally speaking for two-seat attack/trainers like Tucano, TA-50 or A-37, it allows a small airforce to perform training and combat with the same force pool.
For instance Honduras has four C-101. If your country is stable and you want to train pilots, no problem, you can use all four planes for training.
The Philippines are getting twelve TA-50, they haven't had jets for a while. So in the beginning, they will need all or most of their jets for training. Later when they have a pilot pool, they can transfer more and more jets to the operational squadron.
And for counter-insurgency or anti-drug operations, it helps to have four eyes.