What is the proper way to merge two MIDI tracks?

When I tried to drag one midi track onto another, the “merged” track became greyed out by a lot of 45-degree black lines. What does it mean? What is the proper way to “merge” two midi tracks? For example, some piano midi files show two right-hand tracks and I would like to merge them to one. Thank you.

You can simply select the Glue tool and glue them. It is done this way for the various reasons that exist not to merge them.