The serious tone is a huge draw to the LKML and that way of working. They really do care about not having left-pad type meltdowns. They really do care about being able to find information easily, even years after the fact.
There's a big difference between shooting the shit in your private communications and cluttering up places where people are looking for solutions.
Contrasting an opinion you don't like with the other extreme is usually called a strawman and is not a good way to argue.
As others have said, I too am not against a light-hearted tone. But when you have a legitimate problem that might be blocking you from doing your work and your only source of information is a GitHub issue then it should go without saying that the information should be dense and compressed and it should absolutely lack memes, yes.
> Go post memes on the LKML and see what happens
I think the seriousness (almost angry tone) in certain communities also is a disservice to attract new members. If I make my first PR in some project, it's easy too feel attacked when the reply is a negative one, albeit strictly professional. If it however has a more light-hearted tone and a bit more sandwiched fun-serious-fun one feels more welcome.