Most of the trading competition are based on trading volume, which instantly discourages or kicks out retail traders. Imagine you, with an account of $2,000 competing with someone whose account is worth $1,000,000. You wouldn't stand a chance.

The exchanges also put in other extra requisites like number of referrals, competitions specifically for new registrants or first deposits

I prefer competitions where winners are picked based on percentage ROI.

Almost of exchanges run trading competitions from week to week, month to months, you just have to keep checking up the announcements.