The NYT had an interesting piece by Sheri Berman on the decline of the center-left in Europe. It points to the sharp drop in the support for social democratic parties across the continent, with many parties that used to lead government barely getting above 20 percent of the vote. Voters apparently see little reason to support these parties. A similar story could be told about the center-left in the United States, although the money they command may allow them to still control the Democratic Party.
To carry her observations a bit further, these center-left parties have been largely complicit in the policies that have redistributed income upward over the last four decades. Tony Blair in the U.K., Gerhard Schroeder, and Bill Clinton were all associated with policies that benefited the financial industry at the expense of the rest of society.
The center-left parties have all been supportive of longer and stronger patent and copyright monopolies, which give money to Bill Gates and other incredibly rich people, as well as more educated workers generally, at the expense of workers with less education who would provide the traditional base for center-left parties. These parties, especially the Democrats under Clinton, supported trade deals which were designed to redistribute income from less-educated workers to capital and the most highly educated workers.
And, these parties have generally supported fiscal and monetary policies that have had the effect of keeping unemployment high in order to minimize the risk of inflation. By reducing workers' bargaining power, these policies have put downward pressure on the wages of the bulk of the workforce. (Yes, these points and more are covered in my [free] book Rigged: How Globalization and the Rules of the Modern Economy Were Structured to Make the Rich Richer.)
Anyhow, it is not surprising that workers will not support political parties that are committed to taking money out of their pockets and giving it to the rich. If this continues to be the agenda of center-left parties, they are not likely to have much of a future.