the problem I see with this bet is that even the chance is 1 in ~30k the user can win it in his first bet before the 29,999 losing bets. or what do I miss here?
What you're missing is that on the other hand the same guy could make 99,999 losing bets in a row and never hit the 121x payout.
It's a gamble, and nobody is saying the investors always win.
By using the Kelly criterion the house is optimising the expected returns for the investors. That doesn't mean the investors won't be making a loss at times.