Well, I can see many reasons why they didn't have Mello or Near.
1.) ending the movies with L satisfies the L fans
2.) its easier for the movie makers (less movies)
3.) killing L lost Death Note lots of fans
4.) it would confuse a normal, non-otaku audience
5.) thus the movie would lose money
6.) L was supposed to win in the original story anyway
7.) L didn't win in the manga because the writer was asked to extend it
8.) Mello and Near aren't as easily liked as L
9.) It further differentiates the 2 projects
10.) giant sagas are rarely successful
Personally, I like the way they ended the movies much better then the manga version.
