I wonder if this is cyclical behavior. We had a year like that last year down in NJ. This year it was back to maybe only a week. I live in the west part of the state surrounded by parkland. Rainfall was the only thing that was dramatically different this year. Last year was extremely wet spring and early summer (when they appeared) followed by an extremely dry end of summer into fall. This year we've had average rain in almost every month. The rain evidence isn't anecdotal, I have a state rainfall gauge a couple miles down the road from me with records going back at least a few decades.
One of my favorite memories of cycling through the midwest in the early 90's was watching the redwing blackbird population slowly recover.
Most individual people won’t feel the change that’s happened over their lifetime unless they’re wondering why it doesn’t snow any more or how they ever managed without air conditioning; it shows up in higher costs for national-scale-multi-year weather damage or crop and fishing productivity.
And of course, this is a global rather than local effect, so some places have more change than others. My first trip to the USA was the 2014/15 winter when there was simultaneously record cold on the Atlantic coast and record warm on the Pacific coast.
I'm not sure why it was a good season for them. Like you say, traffic, lighting, pesticide sprays on farms, all really the same despite COVID. Reduced air traffic I don't think would have an affect? Even after I sprayed my vineyard with insecticide to deal with japanese beetles they were fine, and continued to prosper in and around there.
It may just be that we've had an unusually hot dry year, I assume where you have as well. Maybe that's advantageous for them somehow?