When he bets 100 and loses he bets 200 , if he loses that he bets 300 , and thats it , he doesnt have 400-500-600 bet options , hence when he loses 300 , he bets 300 once again which keeps him from a losing streak bust . He could lose like 10-15 times and might still have enough coins to comeback
This is a good point you make.
This is very important to understand. Most players go bust because there is nothing stopping them from betting their entire bankroll in one hit. Nakowa will take longer to bust because he cannot in any way risk 5,000 on 2x payout at once.