I haven't actually watched movie 11 all the way through yet, but I presume everything was kept ^^
Simply put, the movies are operated on a much larger budget. Look at the quality of animation compared to the series at the time any movie released (besides Movie #1, which had animation even WORSE than the early parts of Kanto). More money means they can use the music and pay for the rights a bit easier and justify the cost.
That's a popular idea, but there's evidence that negates it:
Specials
- Chronicles kept no original BGM (only 4Kids non-movie to do so)
- Mastermind of Mirage Pokemon kept all and only original BGM (first non-movie to do so)
- Pikachu's Island Adventure kept no original BGM (only PUSA dub to do so)
- PMD2 kept all and only original BGM (can't remember PMD1)
- Pokemon Ranger 1 Deoxys had a mix of dub and original BGM like normal episodes
- Pokemon Ranger 2 Riolu episodes kept all and only original BGM
Movies and TV
- Movie 9 replaces a track
- 4Kids Movie 1-3 have no original BGM and the shorts don't keep the original BGM (I know this is true for the 1st short, not sure about 2 and 3 because I haven't watched them)
- Movie 5 (from what I remember) replaces the opening title theme but keeps in a Japanese song exactly as it was - never been done before or again
- Movie 6 is the only film to have the same ending theme as Japan - they translate some of it and keep some in Japanese (perhaps because the song May hums and the BGM goes along with the song?) and they actually dubbed Polka O Dolka
- Movie 7 replaces the ending theme and all the instrumentals of the Japanese ending theme throughout the movie, which is kind of opposite what happened in movie 6
- They don't keep the movie tracks in episodes that they have used in the movies
- 4Kids sometimes kept original Japanese movie 1 tracks in episodes and, rarely, movie 2 tracks in episodes, despite not using it in them in the movies
- 4Kids actually used original Pokemon BGM in other shows they dubbed
- They'll dub songs that the characters actually sing with the original BGM but won't if it just plays in the backround (Takeshi's Paradise, Team Rocket Forever, Nyasu no Uta) - why not change the background music, too? Except they kept "Gotta Dance" in the background which of "King and Queen for a day" the only song completly dubbed through
- - - They keep song instrumentals which surely must cost more than "normal" BGM
- such as Advance Adventure (both 4Kids and PUSA) OK! (only 4Kids have kept this) Poketaari Monsutaari (only PUSA) and PUSA kept the karaoke version of "Watashi, Makenai!" when they didn't "need" to but when it plays with the actual song, they didn't replace with a karaoke version (DP May returns)
- PUSA replaced "Team Rocket Forever" with Japanese lyrics playing with a karaoke version - never done before
- Music that is kept varies tremendously from episode to episode with PUSA from DP, tghe lowest being 2 (Dustox's leaves) and the highest being 17 (Dawn's Early Night)
To the dub, at least, surely movies are like an extra long episode because all they have to do is dub. Do they really need more money for more dubbing? Would their music budget be bigger just because it is a movie if all they're supposed to do is dub? I actually don't know what the answer is.
From what I've heard from Dogasu, usually animes tend to keep all the original BGM, or none of it and Pokemon is quite rare in using both dub and original BGM. Not sure if I've remembered that correctly.
Anyway, what I think is that 4kids couldn't be bothered to make up new music for every movie after the 3rd. All the dub music 4Kids used in AG (except the songs) were made in season 1 or movie 1 or 2. They've only used movie 3 music in that movie, I think. I have no idea why either. PUSA have made their own music, and they said this was to make it more "hip" (not lying) but PUSA have added improved tracks through DP and improved it a lot in Battle Dimesion. But why bother when they could keep the original BGM? I dunno. I think the evidence shows that they have enough money to buy the music, they just don't want to. Movies are going to be more commercial the episodes so I suppose they'll spend more money to buy it. But even the evidence there is completly contridictory since they'll use movie tracks in episodes that they didn't use in movies and will add music where there was originally silence.
My conclusion: they're all crazy. I don't know whether they just think they're improving it or what.