Option to separate Midi region by note pitch not available, only by articulation

I am having difficulty figuring out how to separate a MIDI region by note pitch. I'm ultimately trying to separate a drummer region that I converted to MIDI. When I highlight the track and go to edit-> separate midi region, the only available option is to separate by articulation.

I moved the MIDI region to a different MIDI track, but it didn't make any difference.

I've include a picture of what I am seeing here.

I'm assuming there is something simple I'm missing here. Any help appreciated.