Great questions, T!
Manga publishers and artists who self-publish doujinshi typically self-censor their work to prevent it from running afoul of Japan’s vague, completely non-specific obscenity law, Article 175. Article 175 has been part of the Japanese penal code since 1907 and has been used to incarcerate as well as extort fines out of artists who don’t comply with the arbitrary obscenity standards of the day. Before the 1990s, the entire pubic region had to be obscured. Today, usually a black bar will suffice in covering what’s supposedly the most “obscene” part of the male body - the glans. But the standards of censorship fluctuate - sometimes stricter censorship is required, and at times enforcement has become more lax. Recently, censorship has been on the rise in the buildup to the 2020 Tokyo Olympics - so artists are in real danger of being arrested if their work offends the sensibilities of the Tokyo Metropolitan Police.
As for uncensored versions, they can and are being published in foreign markets! The Passion of Gengoroh Tagame presents gay manga without censored body parts, as does our upcoming anthology Massive: Gay Erotic Manga and the Men Who Make It. Usually manga artists add censorship measures to their work after the fact, on a separate Photoshop layer if they’re working digitally. There is one story in Massive that retains its black bars, because it was drawn on paper and the bars were applied directly to the page. But legally, we are free to show as much cartoon cock as we want in the United States! These days, Japanese artists also have the option of hosting their work on international servers (like Tumblr) where they are only beholden to the site’s Terms of Service. Hence, the glorious plethora of penis on Ebith’s Tumblr. Thanks, Yahoo!
For further reading, check out the “Censorship“ tag on Gay Manga!