Regulating participants to only those who have a purpose and meaningful reasons, would mean higher bid-ask spreads, less liquidity and less turnover, which then means those markets would probably cease to exist. Gamblers in these special markets are a net-positive, non-gamblers are happy to give some gamblers a payday or some drink money, since it allows non-gamblers to focus on their main activity, instead of doing their activity and gamble that everything turns out fine.