Why do my Blu-rays have both DTS-HD MA and a DTS versions of the same audio?

My understanding was that all the various versions of DTS were backwards compatible - e.g. DTS-HD MA is built around a basic DTS core. So I'm not sure why my blu-ray rips have two copies of the main audio and two copies of the commentary audio, one in DTS-HD MA and one in DTS. Is it just because they're not literally/completely backwards compatible, i.e. older equipment just won't be able to read the DTS-HD MA track at all, even to extract the core? Or are they actually just one track on the blu-ray, and it's only because I've ripped it to an MKV that it's been separated into two for compatability reasons?

it is needed because there is a case where no audio could be played so a DD or DTS stream needs to be present except for stereo only. sill a good question because i think the core of DTS-HD MA is not DTS but lossy DTS-HD so DTS or DD is still needed.

Hi there. If you're looking at your Blu-ray via some decryption application, you should see a listed DTS-HD and listed DTS stream for each real DTS-HD stream. This is because, as you have said, DTS-HD is an extension around legacy DTS. The decryption application in question is simply making it easy for you to extract the core stream by itself if you so desire.