It will take some serious patience to mentally work through the gray area here, and that's not a strong point for folks on the internet, but I'm gonna go there anyway, admittedly with a bit of a wince.
Obviously, abuse of any kind is worse than the kind of gambling we're talking about here - and smoking weed, for that matter. The punishment in society should be far greater for those more heinous behaviors.
But the gambling and the drugs (can) have direct impact on the league, its teams, the games and the results. That's why there's such a clear picture of what can/will happen to players who engage in those behaviors.
If you want to suggest that stronger penalties should exist for players like Ray Rice, Kareem Hunt, Adrian Peterson and the like, I'm actually all in favor of that. But it's explainable and understandable that the league has harsh penalties for gambling and drugs.