once you sell, your profit/loss dosen't count towards the rankings.

 

The rankings aren't based on % gain, but the amount of the gain. The person up 1% and $100,000 is on top of the person with a 100% return.

 

If you traded your shares in, your profit margin will be adjusted based on the rest of your portfolio. As shown in your screenshot, it says you no longer own any of that specific stock therefore resulting in your net profit (amount you earned) to go down causing you to become lower in ranks.