In philosophy 101, my professor said that philosophy was focused on controversial topics because once you could prove a side, it would become science. E.g. the heavens used to be a philosophic topic until we had the ability to prove heliocentrism.
Math is much more focused on the realm of what can be proved. Unproven statements in math (e.g. conjectures or axioms) are the exceptions that prove the rule.
Professional mathematicians spend their lives working on the unproven. It just seems like math is about what's already been proven because it takes so much education to reach the unproven ideas and unanswered questions.
I don't think this is a clear conclusion at all. Philosophy is inherently very political (all political ideas ultimately come from philosophy, after all). Philosophy is also concerned with the real world and human affairs much more than abstract math is.
It's also funny that you bring up post-modernism, a philosophical current famous and often ridiculed for being one of the most deliberately obfuscated.
I also know that a lot of the efforts of brininging mathematical thinking and abstraction in the humanities end up exactly in obscurantism: most of the field can't understand it, but it has cultural clout so they can't admit that, and it becomes a source of empty prestige, with maths literally sprinkled on studies just to access that clout. Even in medicine, math-y papers are/were often accepted unconditionally, with peer review unable to check the actual maths, but unwilling to admit their lack of mathematical culture. For an example, there was a medical article published in 1993 [0], which is a re-discovery of the trapese method of integration. This got around 100 citations.
Of course, that article is at least correct. In postmodern literary studies, there is a famous example of an intentionally meaningless, but very abstract and complex sounding article that was successfully published in one of the leading journals, despite ultimately being gibberish [1].
My utlimate point being, I don't think there is any link between obscurity of a field and its resistance to internal or external politics.
[0] http://care.diabetesjournals.org/cgi/content/abstract/17/2/1...
[1] https://en.m.wikipedia.org/wiki/Sokal_affair