Berets have features that make them very attractive to the military:
(1) they are cheap, easy to make in large numbers,
(2) they can be manufactured in a wide range of colors,
(3) They can be rolled up and stuffed into a pocket or beneath the shirt epaulette without damage, and
(4) They can be worn with headphones (this is one of the reasons why tank crews adopted the beret).
However the beret is not so useful in field conditions for the modern infantryman, who requires protective helmets, and is usually not seen worn by infantry on operations.
Military beret - Wikipedia, the free encyclopedia