Bra usually look like a cage for me, with straps crossed looks even more uncomfortable!
Most Helpful Girl
If you're talking about a racer back bra? Its so that the straps won't slide from the shoulders. Its also less restricting to the arms and shoulder blades. Its very common staple in women's undergarments.
Or you could be talking about the strappy sports bra trend that's recently been hot in women's athletic wear. It has no purpose other than for fashion. Its not as uncomfortable as it looks.