1) He/she is in a meeting, they have a choice - to or not to reply
2) If their screen is shared, I am not disturbing the meeting attendees making them read what I typed, and what comes in the notification pop-up
3) Gives enough time for the other person to switch context
4) Ignore me for an indefinite amount of time and continue their work
If the other person responds, my second comment would be with full details.