Why are some people chronically late?

Please, can someone explain this to me? Why are some people chronically late? I need to know.
Middle Cat was supposed to take the Senior Cat somewhere yesterday. She was late. It was not a good start to the afternoon. They needed to be on time for the appointment. She knew that. She was still late - without a good excuse. I will draw a line there and say no more. 
For three years I babysat every Tuesday night for a family so that the mother could go to orchestra practice and the father went to an evening university lecture. It was one of the ways in which I managed to earn just enough money to go to teacher training college. 
I would arrive in the late afternoon. I would help bath the children ( and "don't let the twins sit at the plug end"- or the water would mysteriously disappear down the drain). I would hear the older two read from their school primers and do their homework. I would supervise the eldest while she set the table for the evening meal  while I watched the twins and helped the second one clean everyone's shoes for the morning. 
Their father would arrive home from school about five and there would be a very early meal before the two adults disappeared. The eldest two would look at me after their parents had gone. They didn't have to say anything. We all wondered what their mother had been doing all that time. 
She wasn't lazy. She was anything but lazy. She seemed to be on the go all the time. We just couldn't work out what she did. Things just didn't get done. She would rush from one thing to the next and the first thing would not get finished. 
After she had gone the eldest two would help me tidy up. In half an hour the house would be tidy apart from the toys the twins had been playing with. Then they would all pile into their cots and beds and I would read two stories - one for the twins and one chapter of whichever book the older two and I were reading at the time. 
Then I would settle down and  do whatever work I had planned for the evening.
Right through those three years the father only got to the university on time because he told his wife that the lecture started half an hour before it actually did. It was the only way to make  sure she got to orchestra practice on time and for him to get to university on time. It was the same for everything else. People knew them well enough to tell them things started earlier than they actually did - just so there was some chance of them getting there on time. 
I know other chronically late people, one as bad as the one I have just described.
It's not good. I don't like being late. I try not to be late. I'll get somewhere early and lurk  around the corner rather than be late. I don't like being early either but, as I don't drive, I have to depend on the train or a taxi or the person who is taking me somewhere.
But I don't  understand what makes people consistently late. I know there are times when it can't be helped but to always be late suggests something else is wrong. What is it?
If someone can explain then perhaps I can explain to the Senior Cat why Middle Cat is often late too?