Both sides of the issue have their reasons.
I mean, on one hand, it's obvious that if something important comes up, you can't be expected to show up to the DnD session. No duh. This isn't the problem.
On the other hand, when the DM does 90% of the work, it's reasonable for them to get a bit peeved if the player doesn't do the 10% (that is, showing up at the session).
When I put all the work and give you multiple sidequests and different areas you can choose to go and explore and detailed npcs, and you tell me you're too busy to play that day..... I think "well, then I guess -I- was not busy enough for you since I did all that work for you to enjoy! Only your busy time is important but mine doesn't matter?".
And this is why the problem is that I'd like to have an -idea- of the reason that player is not coming. I don't need to know your personal stuff, I just need to know for sure it's not like you didn't show up only because you were in a bad mood or because you forgot of a dinner party or some other frivolous motivation.
Because if you're telling me you can't commit to the 10%, I won't commit to the 90% next time, not for you.