I can finally articulate why I don’t like subscribe forms in the middle of an article: they invade the content space.
Yes, modern web is full of advertisements, self-promotion, branding, regulatory banners and other “product techniques”. Such is life. Most of them occupy their own space. Banners are on different layer. Marketing is usually before or after, or always visible on the side.
But inline subscribe forms are different. They live inside the text itself, and that pisses me off. You have no right! A person is talking to me, and you dare interrupt our dialogue? Get off our lawn!