I have come across the following sentences where the first one is correct and second is not correct
어제 아파서 못 왔어요. (O)
어제 아프니까 못 왔어요. (X)
I can understand that 아/어/여서 can't be used for imperative or asking someone to do something while 니까 can.
But I find it difficult to grasp the other difference between them, and the more I read the more I get confused about the "objective vs subjective" and "own feelings / situation". If 니까 is for "subjective reasoning", then suppose one was sick, actually some people may still choose to come, and some may choose to not come. So there is "subjective reasoning" here. Then why the second sentence is not correct ?