Yanbu, being constantly late is very rude and annoying.
However I don't think it's always a sign that the person doesn't give a shit. I certainly can be, but some people really do have a poor perception of time.
I've been guilty of being late, I definitely don't do it deliberately, it makes me stressed and embarrassed, but I am bad a judging time.
It sounds so obvious, like I need to leave the house at 7.30, I'm ready for 7.30, but I've totally underestimated the time it takes to get everyone's shoes on, an unexpected trip to the toilet, grab the bags, load the car, by which point I am of course 10 minutes late.
It took for me to read about it online to realise where I was going wrong, I've managed now to be on time, but even now it's hard to break the habit.
When I leave actually on time I always imagine I'm going to be really early.