The whole movie seemed to be a victim of poor/misguided marketing:
http://officialfan.proboards.com/thread/476856/good-movies-marketed-ba dly
http://officialfan.proboards.com/post/9816389/quote/476856
Josie and the Pussycats, it was a movie ripping late 90's early 2k's to shreds, and they marketed it directly to the people they made fun of and not to the non-mainstream music fans. Every punk rocker I have known has loved that movie.
http://www.imdb.com/board/10236348/reviews-64
"Josie and the Pussycats" was a great satire of our "mass consumerism" society. Many criticized the massive product placements. I think those people missed the point of the movie. In a good satire, sometimes the humor is missed (ex. I totally missed the humor of "Scream", I still think it is just another slasher flick) because the satirization becomes the object of the satire. The movie was marketed to the 10-13 year-old crowd, but the humor was aimed toward adults. If it wasn't marketed as a "chick flick" for 10-13 year-olds, it might have done better.

The only thing the two have in common is the title.

My guess is because the audience of the original show were adults by the time the movie came out so they catered to the original JATP fans.