Lady GaGa has not only been a more obtrusive figure in the music industry, but her every appearance is a cause for cameras. her outlandish costumes excite everyone, whilst when she doesn't wear one it's even more of a reason to snap a picture!
Ke$ha is just your average artist; you won't find paparazzi at her door night and day, and you could probably pik up the clothes she usually wears in your average clothing store.
Therefore, there are more pictures of Lady GaGa because her style is more interesting, and every outfit she wears has something new to be immortalised.
NOTE: This does not mean that GaGa is better than Ke$ha, musically or in her fashion sense, it's merely the truth.
Because Lady GaGa has been in the spotlight/ music industry longer than Ke$ha has. I mean duh! Lady GaGa had her first album come out in 2008 & Ke$ha's first album came out like just a few months ago. & even before then, there were lot's of pics of GaGa anyways, so that's why. But Ke$ha will end up will more pics just like GaGa so you have nothing to worry about.
Here, I'll post a pic of her just to make you happy:
Lady Gaga has tons of different crazy outfits that are picture worthy. She has also been around longer. And she is probably invited to more photo shoots for magazines and other companies. Ke$ha doesn't have the outfits, the time or the popularity to have as much photos.