This is just my personal opinion, but I think bomber aircraft have more ethical issues associated with them than fighter aircraft, and so are probably less popular. Spitfires are strongly associated with defensive actions like the Battle of Britain, so it's easy to see Spitfires as a good thing. 

Explaining to a child at an airshow what a Lancaster was sometimes used for, such as [the WWII bombing of Dresden][1] is more difficult. ["Bomber" Harris][2] who was in charge of Lancaster forces remains a controversial figure.


  [1]: https://en.wikipedia.org/wiki/Bombing_of_Dresden
  [2]: https://en.wikipedia.org/wiki/Sir_Arthur_Harris,_1st_Baronet