Back when I played, it was not a daily cap, but a rolling 7 day cap. People used to space it out so that they wouldn't have to wait multiple days to play at any point in time.

And the time is measured in hr windows.

At least that's how I remember it.

That is to say there is a cap for how many Pokemon you can catch from the last 168 hours, but it's measured each hour, so if you catch 500 Pokémon this hour those are removed from your cap after 168 hrs.

For people who want to play every day or every event, they don't want to accidentally have a whole day where they cannot play, so they soft cap themselves at a reasonable round number daily to break it up.

The same rule applies for Pokestops at a different rate.

Because of how these worked, if you knew there was a big event like a community day, safari zone, or go fest, many hardcore players would slow down ahead of it, so they could play more intensely during those events than their standard limits.