Its the mentality of english public in general. Its just like the soccer (albiet the cricket side are a lot more competitive globally than the english soccer team), where the expectation rediculously outweighs the talent of the team. If the press and the entire country looked at their chances logically they wouldn't put so much pressure on the team.
The english team on paper are better than the aussies at the moment. So they deserve to be favourites and will probably do well this ashes series (probably will win - unfort. for me
). But england havent won in Australia for a looooooong time and people in england seem to overlook that.