Why arent Hijack and assassination missions Fissure options?

[Cody]

Assassination is probably close to the same speed as a capture mission or slightly slower with the exception of a few bosses. why cant we run random assassination missions as fissures?

Hijack would probably be as fast as interception missions and its fun to ride the vehicle, why cant we have this as a fissure option also?

we currently have only half the missions available as a fissure i feel there should be more.

[GPrime96]

I'm guessing DE want their Fissure missions on similar missions that's in the Void (Capture, Interception, Survival, Exterminate, Sabotage). But at the Same time, Excavations get fissures too so IDK.