Lastly I've seen this also be depicted as mud from a breaking dam in some stories so it might also be a primordial fear of the effects of flooding waters destroying something but i like my tar metaphor

As for the why, its as you said, an easy cultural short hand for something that consumes others, be it despair, Sorrow, Hatred, Rot, or Death. As for why that shape, as i said above, its tar that moves, that grows, that can fit into any space, but more importantly all spaces.

To expand on this, the oily texture yet liquid form is a way of having it be able to be in any space yet also linger where it has already been. Black and purple are also the colors of bruised or necronic skin so the color choice makes sense to me.

Im not sure which one to actually comment on so i picked here.

My understanding has always been that "The ooze" is visually similar to tar pits as once most things land on it they get sucked into it, with extensive amounts of eyes linked to a predator or the viewer/subject being studied.

The second paragraph is hard hitting.

Your fine to be angry, sad, etc & youre even allowed to harbor emotions that would be very shocking to say

But emotions are meant to drive you to do tangible stuff. What tangible outcome do you want to build? Cause destroying is easy, creating is extremely hard. Do the hard tasks not the easy ones

So there's a secret butt rest between the mecha legs, i seeeeeeee.

Wait where are her feet?

Taking a text seriously enough to think about it critically can be its own form of loving it, really. Let me delve deep into your story and think about it until I’ve understood every detail and untangled every plot beat. It’s not an insult to have your text engaged with; It’s actually a compliment