http://mocktheweek.wikia.com/wiki/John_Oliver#List_of_appear...
One of them even specifically told us about his strategy before he started his series of lectures. Basically, when people get bored they stop absorbing. Once in a while he will "trick your mind" (i.e. confuse it), and you will pay attention again. To be honest, its why I know as much about operating systems, locks and threads, as I do.
To make this story relevant. Humor is just that, a trick someone plays on your mind.
My feeling is they're trying to seem like they're your friends, so you feel more engaged and listen and don't mind the bias because, you 'know them, and you accept that trait'. The unattached news delivery was not engaging us psychologically (for whatever reason we may need that) so they came up with this new recipe.
Never the less in other countries I've had news delivered pretty matter of factly --with built in biases of course but the news wasn't chased with comedy satire etc. There might have been irony but anyhow there's something about the need for comedy to make it digestible for us
Maybe it's evolutionary? The people who when presented with a problem were able to keep their spirits up while tackling it perhaps had a better success rate then those who lost perspective on their responsibilities to their own emotional wellbeing.
It's not, but entertaining people is a good way to keep them engaged and comedy is a relatively easy way to entertain while telling.
When the content is dry and the delivery is dry and completely unengaging people just tune out, even if the subject is interesting in the abstract.
Comedy is not the only way, Attenborough is entertaining without being comedic, but it's a good way nonetheless.
And comedians are observers of human nature by trade, so they might have an easier time couching down and expressing more "serious" topics than some other entertainers.
And if in-depth news analysis was something people wanted, well, the Economist would have a much higher subscription base than it currently does.
Same stuff was said seriously but when you hear someone describing with serious tone how reality is absurd you don't believe him.