I think what you mean is that people qualify for 5 points only up until Sunday evening, then it drops to 4 points - as opposed to how it works now, switching to a lower point at 2pm - just before the market opens.
There does seem to be some people who make their prediction no simply on what they think the end of week dow will be, but tactically to ensure they have the best chance of being closest to the final dow value. For example player A picks 10750, player B then picks 10749, and player C then picks 10751 - the chance of player B being nearest to the final value is extremely remote as they would have to hit it right on the nail.
There are probably tons of ways of improving the competition. If you have an idea perhaps you'd like to share it with us here? We can them aim to roll out a new version with all the feedback taken into account.
It's probably because you didn't pick the correct direction either lower/same/higher. Unfortunately if the close on Friday is on the border between one direction and another, and your prediction is the wrong direction but maybe just a few points away unfortunately you won't get any points. The idea is to pick the direction (primarily), and then as a bonus, the person with the nearest prediction gets extra points.