If you get a message, it’s just one of the crowd jostling for your limited attention. Not responding is easy and understandable. Imagine you were in a real crowd of people talking at you at once, at all hours of the day. You might miss a thing or two, you’re only human.
But when you send a message it feels like the two of you are alone in a room. A lack of response is personal. Imagine someone sitting across from you, pretending they don’t hear or see you. What an asshole!
It’s one situation. Both perspectives are true.