Because it makes them feel celebratory just like New Years Eve or 4th of July. 

The simple minds of liberals are fascinated with loud noises and shiny things.

I read an article in my local paper.

Fireworks on the Fourth of July, and maybe a day or two ahead of it are pretty normal.

But we've been hearing them for weeks now.  The paper ran with a theory that way too many people are sitting around at home and bored out of their minds with the Coronavirus job losses and restrictions, and so they are getting into mischief with all these fireworks.