Why don't Western girls like to wear BRA ???

Western as in the USA? I'm a G cup and I still wear a bra in the summer. If you're a C cup or smaller you usually don't have to because you're not very well endowed. We do have many styles of summer shirts though that don't require you to wear a bra. They have sewn into them what is called a shelf bra - a piece of stretchy material that is gathered at the bottom with an elastic sewn in, and this is attached to the inside of a shirt. With some women they can just wear these types of shirts and still be supported (not as well as a bra), but with other women that are bigger, these kinds of tops are something they shouldn't be wearing, simply because the shirts only can hold so much weight, most clothing is made to accomodate a B cup (I'm a seamstress and I see this a lot in patterns) or a 2" difference (same thing as a B cup). So if you take a woman with a frame size of 34 for a bra band and suppose she has DD cups or larger, those tops with the shelf bra are either going to be too small for her cup size, or she'll buy the larger size and fall out because the elastic underneath the bust is too large for her frame.