Why do some people only start caring about messages once it's deleted?

So when messages are left on read or are completely ignored but as soon as the same message is deleted, the people who previously ignored the message, start to hyper-focus on the message, why is that? I've noticed this happening multiple times, with multiple people sometimes and over the years... I didn't pay much attention to it until I realised that some do this on purpose...

Why do some people only start caring about messages once it's deleted?
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