I can give you the answer for the Leftist / Radical Leftist /Regressive Lefties.
It's simple : If you're Leftist, you're bombarded with the idea that things that relate to Social Justice are very serious matters.
You can't simply joke about Race, Sex/Sexism, Intolerance, LGBT, Feminism and other issues of Political Correctness.
They enforce Political Correctness because Politics is very serious to them. These issues are very close to their heart.
These political issues become engrained in their personality.
Their life revolves around their Political Causes.
So basically, Mocking Leftist Ideas is basically criticizing the people who hold those views.
It's like I said
>"I don't like Islam, I think it's a violent Religion".
The average muslim is retarded, so they think that : Criticism of Islam as a Religion = Criticizing the people who parctice that religion.
So Criticizing Islam = Direct Insult to Muslims.
Same with Leftism. If you criticize Leftist ideas, they think you are directly criticizing them as people, their integrity, their morals, their sense who whar is right, what is just.
If you are so heavily attached to these issues, you can't joke about them. "Racism is a serious issue" they say.
So Having Fun = Criticism = Personnal Attack.
Therefore, Leftistsd are banned of making fun of themselves.
The only allowed Humour, or "Inclusive Hulmour" as they put it, is to criticize and dehumanize your oposition.
The best example is LEftist calling anyone at the Right of Karl Marx as a Nazi.
The insult Nazi is used to dehumanize the opposition, but it's okay, because Nazis = Bad Guys, and Leftist = Good Guys, so they rationalize that with : Nazis oppress Leftist, therefore they are "punching up" instead of "punching down", and therefore it is not only acceptable to make fun of the opposition, it's the only approved way of generating humour.
TL;DR Leftists can't meme because they take everything political and themselves way too seriously.