Take poker , it's about skill and luck. Take about lottery it's purely luck, take sports betting again strategy and luck.
Poker has a lot of skill but all the gambling games are strongly correlated to the factor of luck.
You gave some examples and all of them had the factor of luck but some of them the factor of strategy. So gambling is defined by luck and not about strategy because there are sometimes that luck can destroy your strategy.
Maybe does play a part in gambling, but in the view sporting bets which I'm a big fan, Strategy and logic plays a bigger role in winning. Luck is just based on very small percentage of winning, you can't win all your bets solely based on luck, while you stand a chance to win them if logical enough.