Occam's razor may influence speculation that ETs are AI since it simpler for a machine to go from a hover to mach 1.6 in a second or two than to have an exotic drive that negates inertia within a region for an organic being to not get squished flat against the interior wall.
Perhaps there were days when it was somewhat safe for organic beings to wander about but bad outcomes could have changed policy.

A machine could also respond on time scales organics can not approach like the hero in the matrix. They also could control our digital tech with more ease. OUR EXOSCALE CRAY SUPER COMPUTERS may even seem 'cute' to the galactic overlords. I don't know what a digital crush entails but The Star Trek movie explored it with Vger.