Not everyone wants to install third party software and take a bunch of extra steps to clean ebooks to read them how they choose. (blog.the-ebook-reader.com)
My fear is that if people don't buy third party software. (nintendotoday.com)
Least but not last, it's worth noting that custom ROMs are created by third party software developers and they usually come with way more customization options than stock ROMs (official or unofficial). (android.gs)