There's some pretty basic principles in-place we deal with in this reality. You could more or less put them on a scale (albeit, highly subjective) that stretches from Really Positive (good) things to Really Negative (bad) things.
Everybody's train of thought is different, and their range of mobility within that scale is thus, different. Its likely both predetermined (at birth, genetics, ect); and also learned (from life experiences, what you generally expect from possible outcomes of scenarios through conditioning).
So if you were born relatively even-keel, and your life is made-up of generally positive or normal experiences- then your train of thought will lie generally between "neutral-positive" when you try to explain world events.
For instance - with this virus - the aforementioned person will likely and simply explain it away as a reaction to a virus; since this is the first exposure they've had to something that lands this far 'negative' on their scale of experiences - they won't consider conspiracy still, because neither their predetermined state nor their life experience has dragged them their yet.
Conversely- somebody who's life was filled with misfortune or misery is more readily able to seek answers in the 'negative' scale, possibly ignoring the simplistic more 'positive' answers (its just a virus bro) - and more quickly will their train of thought go to "its martial law NWO", "we're about to start WW3", "government is lying" ect.
Its important to remember that all frames of mind in this instance are lacking information; neither is right nor wrong, they're just hypothesis. Neither is mentally ill.
I wouldn't define it as 'mental illness' unless something is scientifically proven to the person and their questions are answered; and yet, they are so rooted in their own frame of mind, that they ignore the science. Hence, reinforcing this poster's answer:
>>9891490This is simple IF>THEN>ELSE logic, which is ultimately mathematic in nature.