Why do left wing governments sometimes support policies which harm their constituents? In A Theory of Political Entrenchment Gilles Saint-Paul, Davide Ticchi and Andrea Vindigni offer an answer:

A partially self-interested left-wing party may implement (entrenchment) policies reducing the income of its own constituency, the lower class, in order to consolidate its future political power. Such policies increase the net gain that low-skill agents obtain from income redistribution, which only the Left (but not the Right) can credibly commit to provide, and therefore may help offsetting a potential future aggregate ideological shock averse to the left-wing party.

The basic idea may also be put this way. A left wing government might not want to pass policies to educate the masses or open markets to small business firms because such policies are likely to be successful and in the process create a class of skilled workers and petty bourgeoisie who will vote against the left-wing party and its policies of income redistribution. By keeping its constituents poor, the left-wing party keeps its constituents beholden because only the left-wing party will support income redistribution.

The left-wing party might even pass policies that the right-wing party wants in order to build its own future power base. The authors give the example of the Democrats under Bill Clinton supporting NAFTA which may have harmed the left-wing constituency of labor. The authors show, moreover, that the effect is likely to be bigger the bigger are political rents and the more stable are political careers. In other words, Bill Clinton passed NAFTA so that Hillary Clinton could run against it. An interesting idea if not wholly convincing.