You drive at 23mph and have done for the last 5 miles.

It's a clear and dry evening on a well lit road. The road ahead is empty, no speed bumps or roundabouts, and there is a growing trail of traffic behind you.

You approach a speed camera, so you drop down to 18mph.

After passing the camera, you go back to 23mph.

People who do this.... can you please clarify why?

Edit: I do the same journey 2-3 times per week, and it is more common than not that this happens... almost every time.

Edit 2: For clarity... a lot of people seem to be missing the point. I'm not asking "why are people driving below the limit?"

Yes, we know it is a limit and not a target. (Note that you can fail a test for "obstructing the flow of traffic" if driving significantly below the speed limit)

My question is "when already driving below the limit, why do people drop their speed even more when approaching a speed camera, and then speed up?"

They are already significantly below the limit. There is no way they are getting flashed. Why slow even more?