Why does an mercury ore exist as HgS? Cinnabar($\ce{HgS}$)  is one of the most common ores of mercury.
Why does it not exist at $\ce{HgO}$ or some other such compound?
Is there any reason for why it is so prevalent?
Does it react less with other compounds, or maybe due to some solid structure of HgS having some characteristic property giving it more stability?
I'm seeking an explanation without the mention of free energy, because it doesn't properly explain the phenomenon for me. I understand that cinnabar is abundant in the crust, and my question is why is $\ce{HgS}$ so common?
Why $\ce{HgS}$ and not $\ce{HgO}$?

Because of HSAB. F'x has already answered a previous question of why mercury has propensity towards thiols(or in general sulfur). Quoting the relevant information:

In Pearson's HSAB theory (hard and soft acids and bases), the reason
the $\ce{S-Hg}$ bond is be stronger than the $\ce{O-Hg}$ can be
explained because $\ce{S^2-}$ is a soft basis and $\ce{Hg(II)}$ is a
soft acid, making a good fit while $\ce{O^2-}$ is harder.

If this answer helps, please make sure to upvote F'xs answer.