Why were the Conservatives (UK) unable to win a majority in 2010?

[Don Vito Corleone]

Labour had been in power for 13 years, Brown was unpopular and uncharismatic to boot, the economy was doing terrible, Labour had led the country to an unpopular war, and Cameron was a young fresh face for the Tories who had moved them closer to the middle of the political spectrum, plus he was quite good at communication. In spite of all this, not only was the election not a landslide, but Cameron failed to even win an overall majority. Why was this?

[Don Vito Corleone]

So it appears, reading through some of the responses on this thread, that Labour was very fortunate with their 258 seats in 2010. Given how bleak things looked for Labour even a year before the election, I would have to agree.