How hard is it to be cordial and pleasant while you are struggling?

I live and work in the Washington DC area and the area has been going thru a lot lately. Layoffs, local economy struggling, Trump policies have negatively impacted many ppl. If i would put ppl who lost their job aside, I am getting the impression there is a large group of ppl that are overly pessimistic even though they have a decent job, healthy, family, etc.

I am not trying totally judge based on my assumption but trying to understand why is hard for ppl to be pleasant/positive in their interactions when they have so much good things happening in their lives. Everyone looks grumpy and mad at the world, even at my job and I know most of the are getting paid well