Often that selection pressure works towards less dangerous variants because that gives them more opportunity to infect others.
Sometimes a virus kills off everyone who is susceptible to it. So it's now less dangerous to those who remain.
In the caae of Covid, it is infectious long before it kills, and so there is no great selection pressure for it to become less dangerous.
https://www.politifact.com/factchecks/2021/dec/08/facebook-p...
I personally credit the prediction attributed to Luc Montagnier back in 2020 that because COVID exhibited unnatural characteristics that exacerbated the severity of illness, he predicted that over time the characteristics would evolve out of the virus and result in a more benign illness. This is a reason why it would have been useful to have a scientific debate over the lab leak theory, because the origin of the virus informs our best guess of the path it may take in the future, which has so far confirmed to this prediction.
HIV is an interesting case because it is "just a flu" for a few weeks, then remains contagious but isn't severe at all, until it develops into AIDS years later.
Thank you politifact.com political fact check fact check for checking that.
That's probably only in the case where the disease is so severe it kills the host before it can spread very easily, not some general rule.
Let's say you have a virus that's super contagious for two weeks with no symptoms and nearly everyone who gets it dies within a month. What evolutionary pressure would it be under to change as long as it has fresh hosts to infect?
Of course, more severe variants can always develop. Holds same for flu, HIV, ... not just COVID.