What's ironic is that the complete opposite is true to an extent---when you are playing a +ev game you do need discipline and bankroll management(obviously) when you're playing a -ev game and your goal is to make money you should just bet everything on one throw of the dice or on flip of the card---the logic being that you have the best chance to double your money by just going all-in. When you martingale the more martingales in your sequence the lower and lower your probability becomes of doubling your initial bankroll. Obviously i would NEVER recommend either but if you have to do one the latter is the way to go...If you aren't playing for the rush or the fantasy but just about money.
The reason these people(along with CM himself) believe a big bankroll is key is that they believe they will get enough sequences in their martingales that it will be impossible to lose that many times in a row. It isn't!(obviously)