> Why not just blast him or put him in one of the presses or
> one of the big melting vats?
Because there is some curious, sentient being(s) who is interested in him.
I'm guessing that those feet he saw belonged to a life form. Sure they were metallic, but do you think humans would wear air jordans in a practically atmosphereless environment? What do our astronaunts wear in space? Even if there are no humans on mars, those feet belonged to curious creatures. An unintelligent machine would have focused on its task of catching the intruder, especially when something got blown up. Unless something (again, sentient and curious on Mars) ordered these legs away, they must have been curious.
If something did order them away, I'll bet that it is curious. Somewhere in there there is an intelligent sentient being (maybe AI) that knows about zach and wants to learn more. It is confident enough in its supremacy to not destroy the first small threat, so we should definately be careful.
Who/whatever it is, I'll bet we'll meet it soon.
Hamlet