How come girls say they only want friends and are never looking for a relationship?

Most single girls never say they're looking for a relationship. It's just something I've noticed. They always say something like I'm looking for a friend. So why don't they want to seem like they are available for a relationship?

My thought process is girls think it looks desperate to beg for a relationship. But what ends up happening is the guy that they actually like. See that she's not committed to anything and sleeps with her and now all of a sudden she's ready for a relationship.

But she hasn't realized she played herself by not being open to one in the first place. Because if she was she would only attract serious guys that are looking for the same thing.
How come girls say they only want friends and are never looking for a relationship?
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