Simple
Because Labor won so resoundingly in 2007 and Labor had a large majority in most seats.
The liberals did very well to come back as far as they did. Even Kevin "747 again" Rudd, had a 9% swing against him this time.
Rather than the election somehow being used as a criticism of the Liberals, more emphasis should be placed on just how poorly Labor performed.
It was a disaster for Labor. Can't be described in any other manner.
cheers
