Why do some digital movies not have 5.1 surround sound available?

[MrHT]

Originally Posted by steve_dave

The studio/distributor provides the digital file, some retailers get stuck with older files that either have the wrong aspect ratio or audio is downgraded from the original track. The video and/or audio can also have an error that the studio would have to fix.

Broken Arrow 1996 is stereo via Apple & Movies Anywhere, it is 5.1 through Vudu & Amazon. However, Vudu’s file has an error where the audio comes out of all the speakers.

The interesting thing is that TMNT is in 5.1 even on the DVD. So I don’t understand how some digital copies are downgraded to stereo.