This reminds me of the speculative rationalizations that are given after-the-fact whenever the stock market rises or falls.
So let me chime in with the speculation:
The biggest factor is probably the realization that COVID is not as big a personal risk as feared, no matter what the media or the government says. People are gladly using COVID as an excuse to work from home or avoid meeting their elderly relatives, but when it comes to avoiding infection in order to save "the system", enough people simply don't care anymore. It's too abstract.