I’m inclined to think that it’s due to the same mechanisms that cause loss of taste and smell, and vision problems, and neurological issues, and…
There’s quite a bit of literature on the significant oxidative stress from SARS-CoV-2 infection. And on the relationship between oxidative stress and hearing problems.
A complete list of medicine that have been known to cause hearing-loss.
Disclaimer: I lost all my hearing during to one dosage of "quit-smoking" drug. Court case still pending after 8 years.
https://www.europeanreview.org/wp/wp-content/uploads/956.pdf