[ELI5] Why do chicks shave off and draw on (horrible looking) eyebrows?

You only really notice the ones that look bad. Like any other kind of makeup, it takes practice, and your only real canvas is your face.

It starts with having thicker than desired eyebrows. So you tweeze out the ones you dont want. But you have to keep doing it because they come back, but then you get into the habit so much you over tweeze and now you have stupidly thin eyebrows - so you tweeze them all out and start drawing them on

I wish I had the words to express why I dislike OP so much despite essentially agreeing.

Because that's how they'd rather look and your opinion of them (that of a stranger) doesn't really change much of that; live and let live.

It's a learned behavior.

The best example of this I've read before is to look at men with comb overs. so you're young, and you start balding, so you comb over that tiny bald patch and it looks fine, no one notices. But you keep balding and combing over, it progresses slowly, and you've grown accustomed to it. You can't recognize how bad it looks, like the old adage that a frog will boil to death if you raise the water temperature slowly enough. In the end, you look like Donald Trump.

Women tweeze to have sculpted eyebrows, and staring at them that closely in the mirror, and being especially critical of your self image, you identify what you consider to be flaws, and you remove them. You don't see the forest for the trees, you're so focused on each point imperfection and you don't look at the overall presentation, that by the time you quit, you discover you've ruined everything long ago. But you only damage your brow line a little bit, and you use a pencil to fill in and highlight your brow line, and it hides the little damage you do and it looks good and no one notices. Do this over years and you lose perspective, you can't see that you look horrible, because you've grown into this; this is normal to you.

Eventually, you pluck yourself clean, and you've damaged your follicles to the point where your eyebrows don't grow back. Until they start selling eyebrow taupe's, which they actually probably do, women have grown into drawing their eyebrows on. This is normal to them, after years of this behavior. They can't be told otherwise what they have accidentally ingrained in themselves.

And anyone can do this to themselves with regard to anything.

Women think thick healthy eyebrows are masculine and detract from their femininity. So they pencil in some fake ones.