I believe that if we're playing a game with a house edge, where winning depends purely on luck, then bankroll management doesn’t really matter.
Well, open your favorite slot game, press max bet, press spin, and then tell us why bank management is actually good when your play lasted only 1 second and you're down all your money with nothing left to do 
Lol, that's so true!
However, if you do it on a BJ table or in a sports bet, it's different.But then again, who wants to lose all their money in 2 mins?
Not me, 100%! And that's the whole point of having good, tight bankroll management. To enjoy your favorite games as much as you can (and have the possibility to win big accordingly), in a less expensive way.