Relaxed's answer is entirely right about how PrecictWise calculates its number, but I wanted to add some quotes from FiveThirtyEight which may explain why so many people seem so down on his chances. The article was written on 2/19, the day before the South Carolina Republican primary, but given the results there (Trump got all delegates with 32%, Cruz and Rubio split 0 at 22% each), it's even more true.
Cruz’s short-term dilemma has received plenty of attention: Donald Trump is on the verge of a big victory in the South Carolina Republican primary, according to most polls, and could easily capture all 50 of the Palmetto State’s delegates. And if Cruz can’t beat Trump in South Carolina — a Southern state with a large proportion of evangelical and very conservative voters, Cruz’s supposed bread and butter — what “SEC Primary” states can he win on Super Tuesday, March 1?
But Cruz also faces a longer-term, potentially more devastating math problem that has received less attention: The states that are his most natural fits — those with the highest proportions of evangelical voters — are also the least likely to award their delegates on a winner-take-all basis. In other words, Cruz’s votes may not translate into delegates nearly as efficiently as his rivals’.
Effectively, while Cruz may be doing relatively well in the polls nationally, he's only drawing on the support of a certain chunk of the electorate. Those people (primarily evangelicals) are congregated in states that will award someone who wins 55% of the vote 55% of the delegates. So, if the state has 50 delegates to award, Cruz could pick up 27 of them, and the other 23 would be split between Trump and Rubio.
Conversely, in many of the states that happen to have less evangelicals (and/or Cruz supporters), delegates are usually awarded winner-take-all. So if Cruz comes in second (as he effectively tied for in South Carolina), he gets 0.
In addition to that, South Carolina was a very bad sign for Cruz. It was a state that was very demographically favorable to him, and yet he effectively tied for second, significantly behind Trump. If there were signs that supporters of other candidates who are dropping out of the race would go to Cruz, then he might be able to turn things around. But in general, they're not.
Cruz's likely victories will net him less delegates than his opponents will get when Cruz looses... and he didn't do well even in a state where things were favorable for him.