Do you actually find it funny? This is the same joke that's repeated over and over. I can't imagine enjoying it the 500th time. It's more of just a veil for certain beliefs.
For an actual funny (and not so "blah blah SJWs ruining everything") version of this joke, the tv show Atlanta does a much more entertaining version of it, you can find it if you search "transracial".
I don't think people actually expect humor, so much as "I find something in this comic strip that I recognize as similar to something I've encountered elsewhere."