A coach once told me "Give priority to those who give you priority!"

In other words, always give priority to those who respected my time over those that didn't.

I'm usually punctual, even if I know I'll be a few minutes late, I'll make it a point to inform the other party up front. As a matter of fact, I rather arrive early and perhaps just get some light work done first. I always have a few tasks that takes likes than 15 minutes to complete, like data entry or quick research on a topic.

As to why others were consistently late, well, either it's a habit they have, or because in the past, you've allowed them to be late. Some people are just not conscious about time. While I'm punctual going into a meeting, once I'm engrossed, sometimes I accidentally extended the meeting, which could also be disrespectful of other's time too. That's something I'm trying to fix for myself.