Who said betting on a single match is reliable? As we say that the money you deposited in a casino is highly likely to be lost, so is the money you deposited on sport betting sites, regardless of the odds that you go for. Only what people can say is that parlay is riskier, but it has its own advantages.
I think the area which i found parlay betting interesting is due to higher odds possibility.
Which in turns has been saying that people should go for lower odds bets than going to place bet with 10k=100k odds, which i think the winning could be that difficult for the said gambler to win and over with such volume of odds, so people mostly advised that they should be limiting themselves on the total odds they accumulate while gambling.