The stream packing used in the m2ts containers have more overhead than mkv. Basically it uses more data to represent the same a/v streams in a transport stream.
https://forum.videohelp.com/threads/359137-MKVToolNix-Complete-m2ts-to-mkv-reduces-file-size-why
Schorman13 - Thanks a lot dude appreciate the help and the link… 😃