That is true but most gamblers feels they will be losing out completely if they place a single bet, it all boils down to trust and the ability to make more money if gamble separately.
Most gamblers feels multiple bet that is spreading your games makes you more relaxed and stable in other to avoid excess losses and not to get brokendown easily, they feel not all the game will be lost at least one must be favourable to them and less risky than single bet.
Yes, single bet will not gives them much lose but they can manage how much money they can spend. If they thinks that single bet is enough to fills their desire to bet, they will not placing multiple bet.
Maybe it is not best option but it is about how gamblers can be wise to their own money so they will not just wasting on the games. Even they will not know if their multiple bet will win all. Instead risking much money to bet on multiple, they will pick single bet and use enough money they can afford.