it's less risky if you invest your btc in gambling sites it's more stable for your source of income.
Less risky? Having a third party control your coins, where you also depend on that entity to see its bankroll being filled up by people losing to the house, is far from a safe and reliable source of income.
Yes, it's less risk. Investment to earn income is when you trust your money to others. It can be a bank, a site, a person, a business... When you choose a trusted one, the risks lower. A respected entity will use your money well and give you your legit profit.
But when people invest on strange and fictitious business the scam risk is much higher!