Paradox has to have censorship in their games and in this case their forums too because that's what would guarantee a sale in practically most of Europe these days, their primary market. If they were to "soften up" and relax some of their rules, then it would raise a few eyebrows and maybe strain the release of the game in a country and raise some controversy. Yes, some people won't agree with it and call it archaic, but Paradox wants to please us, the consumers! The Hearts of Iron series is a big example of using protective measures like censorship, due to the fact that WW2 is a sensitive topic in Europe, and most countries are divided on letting media (movies, games, tv shows) that shows the evil side go on uncensored, or censor it and/or remove it altogether to avoid the worst (Paradox does it). Since this subreddit is considered a neutral ground, we can post things that would possibly be banned (or get people banned) on the forums, post mods that would be banned (like HPM for Vic2, there's some obscure HOI3 mods that allow a few controversial things, but I lost track of that).
Their biggest "no-no" is:
NOTE: There will not be any swastikas in the game. It IS illegal to show them in Germany and various other countries. Same goes for other Nazi symbols (e.g. related to the SS) or Nazi propaganda material, including songs etc. Any links posted to a mod which includes a Swastika or other illegal Nazi symbols will be deleted. Any threads that complain about this issue will be closed.
For that reason, they have to comply with rules and standards that countries have set in order to not bring Nazisim to light, and since the HOI series takes place before, duing, and after WW2 (1936-1948 for most games, DH has 1933-1964), there's no use of the historically used Swastika Flag the Germans used, but instead, they use the familiar Black-White-Red flag they've used from '33-35. There's no full SS units in the game, but HPP and Black ICE (a mod) has it, but in a smaller degree. Hearts of Iron 2 (German version) took the pictures of the German leaders out and scrambled their names. Sure that wasn't needed, but Paradox took the extra step anyways.
Same goes for AARs, since they too have to follow rules, which is why some people don't post their AARs with sensitive material in the forum, but outside, or on Reddit! It isn't fun to blot/white out tons of mini-swastikas on sprites, flags, and events if you use a mod like that, but it's the rules.
There's also a few other things that Paradox has to keep in mind, like no Holocausts (if it's in game, it'll probably be counter-intuitive, just like in history), no terror bombing or chemical weapons or things like that, Also, for China, I think a few releases were problematic too since they can't have the game show the Warlord states (Shanxi, Guangxi, Guangdong, Xibei San Ma, Yunnan, Si) independent, but a part of Nationalist China (Kuomintang), according to their history. It's hard to please everyone, but those are the rules. Japan also can't have the ingame Rising Sun Flag, since that's controversial too, and offensive to most East Asians (Koreans and Chinese primarily but Filipinos, Vietnamese, Indonesians, Malaysians, Burmese as well) even though it's popularly used by some people in Japan (companies, and right wing nationalists).