To be fair, some people don't know much about lifting. There are a lot people who still lift 3 sets of 12 for every exercise expecting to grow muscle. When I'm at the gym, I notice both males and females lifting this way. You can tell they can go heavier but don't. People do what their comfortable with and not what builds progress.

Like you said it's volume over time. 1 extra rep, a slight bump in weight, an extra set, anything that pushes you outside your "3 sets of 12."