So I’m not a virologist by any stretch, but I do work with computer systems as a profession and think there’s a comparison to be made.
In replicating any given bit of data there’s always the potential for errors. With computer systems there a checks in place but for living systems no so much. The more complex the data amd the more times it replicates the greater the raw chamce to have a particluar bit in the code get scrambled.
So if you have a fadt breeding bug that’s a longer string of RNA than some other the chamce for variants is greater. For viruses, lethality is a byproduct rather than a feature, but since the virus itself has no cognition or control over the outcomes of these fliped bitsthere is an entirely random chance that any given error in the code will either be beneficial, neutral, or deteimental to the propagation of the virus.
To get to what I think is the original question here of ‘did humans create this condition’ I would suspect the answer is no then. For comparison, we still have the ‘common cold’ which changes with the year but there’s never been a vaccine of any meaningful sort issued for it. This particular parent corona virus started off with an abnormally high mortality rate compared to other similar class viruses but seems to have shifted in the last several itterations to a less dangerous (at least in the immidiate semse, long term maybe not) but more rapidly and readily spread form.