gambling can be a source of regular income if you are a good gambler
most places will tax it as income if you pay taxes
but I agree that it's not passive at all... way more active than many other things, and risky too
Who is a good gambler in your understanding?

a gambler that understands that luck won't last forever and that has good risk management
a gambler that is on the positive after years and years of gambling
that should be a good gambler
not sure if they exist, though
I haven't met any