An interesting article.
Covid led to significant changes in human behavior that affects how other viruses and illnesses can be transmitted. Said pathogens are evolving in response. Evolution in action.
I think it’s simpler than that. A metaphor is a callus on your foot: if you hike every day, your feet have calluses and you mostly don’t get blisters. If you stop for two years and then resume your hiking, you’ll get blisters.
Similarly, frequent exposure to pathogens allows the body’s defenses to harden, so it mostly manages to fight them off. Remember that infection typically requires more than just one copy of the pathogen: you don’t get sick because a single COVID-19 virus goes up your nose: you get sick because a bunch do, and overwhelm your defenses.
Disclaimer: I am not a virologist, biologist, or anything like that. This is my understanding from a bunch of reading over the last two years.