Why the fuck do so many girls do this?
For one thing, the vast majority of girls making these posts are just that: girls. They’re young.
For another, we live in a society where a woman’s sexual attractiveness tends to be valued above pretty much everything else about her, yet a woman claiming to believe she is attractive herself is derided as arrogant. So you have a confusing dichotomy where females are encouraged to have as many men as possible find them attractive without actually making claims about it themselves.
Add that confusion to a lack of maturity and the already confusing time of adolescence and you get posts like these.
Don’t resort to imitation but rather look for inspiration to further your own creation in pursuit of innovation.