The second is just that the weather and daylight are improving. I think it was easier to keep spirits up in the spring and summer, as the nights got shorter and the days got warmer. Getting through winter, without the usual seasonal comforts of good company and group celebration, was pretty tough. Now we're through the (literally) darkest period, there's a sense that things are on the mend. (Little comfort to those farther south of course.)
And the third, which really does make a huge difference overall, is the end of the Trump era and the inauguration of President Biden. I was not actually wowed by the ceremony - in particular I thought Biden's own speech was rather fluffy and cliched - but it's such a huge improvement on what came before that I am not complaining much. There's a new normal coming to US politics and also international politics, and not before time.
Feeling in a better mood, I've returned to the scene of my first video from last year with an update.