what is with Yahoo! Answers's serious atmosphere? Why couldn't they have made it a little more light-hearted and friendly?

It is not that bad. If you want serious there are forums like StackExchage where they can downvote as well as upvote. They do too and any flippancy or jokes are downvoted until they disappear. Same with Reddit, but Reddit does have a wider range of forums and characters.

Any funny Questions or Answers are usually left. Generally only political / religious stuff is reported and removed.

light-hearted and friendly went away with the green framework years ago - all nice and supportive user went away or turned into maniacs. The violet/blue destroys a lot and that is planned. You can manipulate the emotions by colours. I saw that the most on here are ignorant; all my answers are 5 stars but nobody is interested in truth.

"Light hearted" to many here would mean anything goes. The further you get away from strict, the harder it is to control. Start on Reddit if you want freedom.

Some users can be very uptight and serious. I think it’s because there’s a lot of older people on here.

I've been using Q&A long enough to know that the atmosphere as changed. No two days are alike in 2020 on Q&A.

Yahoo Answers was always light-hearted and friendly until all those trolls took over. Yahoo Answers will never be the same. 

Hey, look at it this way, it's not as bad as Quora.

im friendly tho 

if you think yahoo answers is serious then that means you are either brand new to yahoo answers or you might be smoking one of the most dangerous substances on the planet