[.577 Tyrannosaur]

If we are to assume that these aliens are indeed mechanical, then they have no 'muscle' to lose. To be sure, even some of the simplest machines and robots on earth are far, far stronger than people, never tire, and are imperious to most harsh environments and hazardous materials... Why would any super-intelligent mechanical being settle for a weak, feeble body when he could just as easily be housed in a nigh-invulnerable, bone-crushingly strong frame.

[11B3]

Machines have their own set of vulnerabilities. (i.e. electromagnetic disturbances)

ETs are possibly just mankind a couple thousand years in the future coming back on a history gathering mission.