Why do a good amount of girls with boyfriends hit/flirt on me?

I noticed a pattern where girls in relationships will check me out and when we have conversations they always flirt or hit on me. With some I end up exchanging number etc, until later through social media I end up finding out they have a boyfriend. These girls will give me a vibe that makes me assume they’re single. I don’t know if I’m giving a wrong vibe which is why this happens often. What could it be.

Why do a good amount of girls with boyfriends hit/flirt on me?
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