Military clothing styles were very different a few hundred years back. Formality often reigned over practical needs and the fabrics available left troops battling certain elements which today would not be a factor.
Clothing also requires more attention and attention and a lot of time is spent on caring for clothes in peacetime, hours that can be used for training to face the challenges of war. You can browse https://www.rddusa.com/product-category/military-clothing to know more about the army surplus clothing.
The colourful and shiny outfits of the parades certainly find their way to the battlefield in the past, if only to ensure that authority is recognised more easily, but this carries risks that must have claimed many lives. A bright red jacket might have helped commanders see that part, but they also helped the enemy identify their targets.
In the desert it is coloured sand, and in the forest are leafy broken patterns, green and brown, the traditional “camo” design that we expect. In addition to design, the economy makes thousands of clothes according to the budget, often with a very tight time span if conflicts will occur soon or even in the process, bringing its own challenges.
Sometimes production exceeds demand or even excessive shipping if the conflict ends quickly and this results in the birth of a military surplus store.