Off the top of my head: not being able to biologically, thinking that they are not able to provide worthy living conditions for the children, abuse in childhood and being afraid of exhibiting the same behaviour, having sick parents/siblings who need a lot of care leaving no time for children, not wanting to increase the burden on the planet... or just plain having the freedom of choice.
It's not a blanket rule and it's more about how you'll feel about yourself, realizing you've been selfish, than it is projecting outwards that anyone without kids must be selfish; that's certainly not the case.
These seem like very clear exceptions and reasons. Take it as a general sentiment, I'm not trying to footnote everything I write online to consider every possible circumstance any human could conceivably encounter. I think you should have known these are clearly not selfish acts. Biologically infertile being selfish? Come on dude.
