>For example, there is a thriving amateur "doujinshi" community that commonly take copyrighted characters without authorization and make porn manga out of it. There are usually sold at conventions like Comiket and can be found second hand in many of these big stores that all over Akihabara.
It should be kept in mind that doujinshi usually make a loss. It's a hobby and not a business. (Also doujinshi isn't just porn)
Doujinshi is a hobby, but that doesn't make it legal, and some companies will go after hobbyists. I may be wrong but I don't expect Disney to allow porn of their characters being sold on the open market.
And BTW, while most doujinshi circles are running at a loss. Second hand shops are for-profit businesses, so there is definitely a commercial element.
As for doujinshi and porn. Last time I went to Comiket, which was quite a while ago, I'd say it was 50/50. And when I say "porn" what I mean is that it contains explicit drawings. Doujinshi is uncommon in the way that there is porn inside but it is not always the main point. In fact many mainstream anime originate from 18+ doujin visual novels with the porn stripped off. Type-moon is particularly well known for that.
The way doujinshi community works is it’s a viral media and talent pool for publishers, and social welfare for manga artists for those make profits.
Disney probably don’t need hand drawn manga artists at this moment, and whether a company do want that pool or how they expect to monetize IP changes corporate stances towards/against doujin.
It should be kept in mind that doujinshi usually make a loss. It's a hobby and not a business. (Also doujinshi isn't just porn)