According to Wikipedia there are 54 airworthy spitfires in the world (30 in the UK alone), yet there are only 2 airworthy Lancasters (Lancaster B X in Canada & Lancaster B I in the RAF's Battle of Britain Memorial Flight).

As far as I'm aware they are similar aircraft (in terms of technology, obviously different size and role) from the same era so why is there such a difference in the numbers?

Is there a fundamental issue with preserving the Lancaster or is it simply a financial/lack of interest issue?