What is up with the friendzone?

I don't get the friendzone at all. My original understanding is that two people are friends, one person likes the other, but the other person only sees them as a friend and is not interested. Simple.
But I've seen primarily men and boys make a big deal out of it and act like it's the worst thing ever.
I also saw this post on instagram, and I don't even want to go into mtgow or @/mtgow_archer, but its like? We're not obligated to date someone we aren't interested in, and we're allowed to date other people and still maintain a friendship with the person we rejected if they still allow the friendship to continue.
I don't see how we're at fault or in the wrong. And what the big deal is.
Can anyone explain the logic?
What is up with the friendzone?
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