They just are, broseph. No one can really answer why whats in style is in style. And yeah, just because you don't like them doesn't mean they'll just disappear out of the universe.
They're not immodest, unless the girls tits are hanging out. I love v-neck and low cut shirts. They're just like, super comfy. You can wear them with colorful tanks and camis, so it doesn't show anything. I do from time to time. But seriously they're so dang comfy and cute. They're very versatile, you can wear them with anything and still look good. And they're really cool in the summer. By cool, I mean you can wear them and not sweat your pores off.