First of all, we must recognize that some people would argue that we have had realignments and new coalition since 1952. For example, some people point to the 1964 election as a major turning point that created new coalitions because it put African Americans squarely in the Democratic coalition and started to push Southern whites towards the Republicans. Other people say that we have had no realignment since 1932.
If we have had no realignment or new coalition since 1952, it is because no major event has happened to force a change. No new issues have come up that could not be dealt with within the party system that existed in 1952. We are still split mainly with regard to how much the government should be involved in running the economy. Nothing has yet happened to get everyone on one side or the other of that debate. Neither has anything happened to make other issues more salient to voters.