Why do you speak about gambling like there is just lucky based games? People lose money all the time in gambling, trading, starting businesses, investing in stupid things, do you know why? Because they get into something unprepared, and I will tell you that preparation is more then half of the work, in many cases even 90%, the best example is betting on sports for that, take 2 house and do a research about the game, injured players, tactics, last games, more deeper you go you will know more things about upcoming game and placing a bet is just couple seconds work, if you prepared yourself good you will win your bet.
With luck based games its about bankroll, you need to have a lot and to make 5% 10%, and to stop, making x2,3,4, more is too much risking you will always lose on long run.
Isn't the word itself more about an activity where you bet your money on pure chance? Of course, there are a lot of games where you also need skills in addition to luck such as, for example, poker and similar games. But in respect to betting on sports, aren't the factors which you speak about already "priced" in? Professional bettors just like bookmakers themselves aren't fools, and they do take into account things you enumerated.