Because there is some encodings that don't work
In one model or another. You will find folk that have discovered that this works here but not there. Then you get to go back to the product manual and you see the list of encodings that is supported and it was sheer luck the other model worked as the encoding was not on the list.
And let's get this out of the way fast. MKV is a CONTAINER and not an encoding format. Some folk forget or never knew that.