A guy ghosted my friend. Why did he do that?

She faced this when she met a guy. At first he was nice to her so she was nice to him too. He invited her out a few and she gave in after that. They continued chatting for a short while then slowly he started taking longer and longer to reply her messages. In the end he totally didn't see her messages at all. Why do you guys think he did this though? I don't know much about this stuff so I'm not sure how to advise her on this

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Correction: he invited her out a few times*
A guy ghosted my friend. Why did he do that?
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