ORB-SLAM for "real-time" camera tracking

Orb slam has been used in robotics for "Simultaneous Localisation And Mapping" for a long time, and they do this in real time while processing data.

I don't understand why the camera solver for motion tracking are so unreliable, when there is technology out there that can do it in real-time with much weaker hardware.

Example of research from 4 YEARS AGO of a drone localising in real-time youtube.com/watch

Here it is done using a CNN at 30 fps: youtube.com/watch

and this paper on MonoSLAM, SLAM with a single mono camera was written in 2007: doc.ic.ac.uk/~ajd/Publications/davison_etal_pami2007.pdf