The thread title says "It's not a trait, you're just rude"
What people are trying to say here is that for a LOT of people, time keeping and executive function is not a desired style, but a cognitive function some people find difficult. Whether they are neurodiverse or not.
If I went to a psychiatrist, with my current difficulties in time management - but I didn't have other areas of ADHD difficulty, I would be neurotypical. I would not have ADHD. I would still be unable to process time and plan accordingly.
My problems in time management are because I am naturally incredibly poor at time keeping. All of the other poor cognitive functions together create the ADHD disorder. It's not a definitive tick box, like pregnant or not pregnant. ADHD is a complex system of difficulties.
Most poor timekeepers on this thread have talked about how hard they find it, how much it bothers them and the guilt they feel. Again and again they're just told to try harder.
I would never speak to somebody with any physical difficulty and dare to call them lazy because they haven't tried my prescriptive way of managing their health. Some people on here have said that they would never be late, but they used to be. Perhaps the late comers in this thread are your "used" to be. It's possible to be helpful without being rude or dismissive.
Not everyone had parents to show them how to manage themselves. Not everyone knows they are neurodiverse. Not everyone finds it as easy as some people. If you work at the problem, and find your own solutions, maybe it's not easy for you. But it still might be easier than for some people who would find it almost impossible.
And as for those who keep repeating that people should just own up to being late. I would pay good money to see you say to someone:
"Dinner at 6? Perfect, I will probably be late though,"
"Oh right, why? What's happening that day? We can move it to another day?"
"No, I'm just really shit. I want to be there at 6 but I will more likely see you at 6.20."
"Shall we change it to 6.20 then?"
"No, because I will still be late then, just keep it at 6"
The majority of people who make plans sincerely hope that this will be one of those times they do everything right.
It's like telling someone who's clumsy "Hey, have you ever just tried harder at walking?"
"Have you ever just decided to not fall over?"
When we're late - a lot of us have just mentally stumbled. Even if we do it all the time.