What the intro to each episode actually says is
They must survive in the most competitive market of all: the high street. But it's a tough trade in tough times.
It's followed by a clip of Sarah how important it is to make money.
The series has been frustrating because of the number of apparently uncommitted contestants and the low standard of some of the food. But no one can accuse the winkers of being uncommitted; they desperately want to win, they don't see losing as an option. I don't want to know the outcome before I watch it but it is fair to assume that the three investors won't invest in a project that's doomed to failure. If the winners are all style and no substance it's because they know that it's a formula that will succeed in the high street.
And by the way, look at some of the big high street chains nowadays. I'm not going to name names but there are some dreadful restaurants around, some of them quite upmarket, and they always have queues out of the door.