Because if that is true, is supposed to be that all gambler who used martingale are now rich, but still no they're not rich still relying on their luck.
that's just half true...
martingale isnt perfect, but that doesnt mean it isnt effective. there's no perfect strategy.
to profit, you will need way more than just a simple martingale... my strategy use martingale but it have particularities and i have my risk management.