Why did this girl leave me on read?

This girl my friend had been trying to get me to date texted me on Instagram she said hey and I texted back whats up and she hasn’t responded and it’s been an hour and it says seen, I’m currently in summer school with her and my friend he told me she liked me but she left me on read so I don’t know if she really likes me or not. (I’m on my brothers account)
Why did this girl leave me on read?
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