According to Matthew Yglesias, it’s got to do with how the Republicans favor policies that the rich like.

“For “you’re going to have to raise the retirement age for Social Security” to count as an “ugly truth” assumes that it’s true. And yet it’s not true. Closing the projected actuarial gap in Social Security requires some combination of more immigration, higher taxes, and lower benefits. Relative to higher taxes, lower benefits tend to be preferred by richer people. And of all the different ways to reduce benefits, raising the retirement age is the one that does the most to punish the poor and demands the least sacrifice from the rich. Christie, it’s true, isn’t saying “whatever the voters want to hear” but he’s not telling the truth either. What he’s doing is saying what rich people want middle class people to believe.”