Why do girls cross their bra straps on their bra under a normal shirt?

I've seen a few girls who have their bra straps crossed like an X under a normal shirt (it was white so you could see the straps)

I know that some girls cross them when wearing like a tank top so the straps don't show, but what's the point of wearing them crossed under a normal shirt?
Why do girls cross their bra straps on their bra under a normal shirt?
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