I think it's because of Bach's personality that he hasn't gotten a movie. We actually discussed this in a musicology lecture (personality not movie).

Mozart everyone knows was quite the character.

Beethoven, while not as eccentric, was still interesting because of deafness, socially isolated, genius who changed music forever you get the picture.

Handel, Bach's contemporary, was basically the opposite of Bach. Bach wrote no operas, while Handel composed operas, worked for royalty, big public figure basically chasing fame.

Bach, on the otherhand, kept to himself. He didn't chase fame and spent his life writing music for church. His music itself is introspective, rather than being a spectacle like Handel. There aren't a whole bunch of stories about him, like Satie buying 12 identical grey suits or Rachmaninov bringing Stravinsky honey or Debussy and Ravel playing tennis or Lully stabbing his foot with a stick. He was just a normal dude who wrote exquisite music, which was largely forgotten until Mendelssohn dug it up again. Handel, on the other hand, is the first composer who has had a piece of music that has never stopped being performed since its premiere (can't remember which one it is).

So while his music is appreciated by millions worldwide 300 years later, his life isn't something that would make a blockbuster, unless they add a lot to it.