There are many reasons that some people are always late--and most chronically late people are late for more than one reason.
In my experience working with chronically late people, most plan unrealistically or don't plan at all. They often have idealistic expectations about how quickly they can do things. Most also have problems staying on plan while they are preparing.
These problems can result from a variety of underlying issues, including "right brain" thinking style, rigid ideas of how things should work, problems with delaying gratification and attention issues.
Some are insufficiently motivated to be punctual, allowing other motives to take them off plan. Some are motivated to be late, e.g., because being late makes them feel powerful.