It’s really, really tough being the prime minister of Japan. Not that many dudes have been able to pull it off for more than a year or two at a time. Koizumi was in office for about five years, which was a miracle, given that the last guy who hung in there that long was Yasuhiro Nakasone, 1982-1987.
With just a couple of exceptions, Japan has been ruled by the Liberal Democratic Party (which, contrary to what it’s name suggests, is a conservative party). Most Japanese have accepted its dominance as a fact of life, and as it goes, this has yielded widespread complacency about politics among the people. Even if somebody wanted to create change, though, it would be nearly impossible to do so because of the faction system even within each party, the importance of seniority, and, well, all kinds of other internal politics.
The guy who explained this all to me while I was a grad student at Columbia was Gerry Curtis, who is probably the #1 Japan expert in the world. If you’re even remotely interested in this stuff, I strongly suggest you read his book, The Logic of Japanese Politics. Total eye-opener.