On the other hand, I've been adjacent to the decision to add them before. You're under a lot of pressure to increase conversion in your onboarding funnel, so you test out moving your email capture up a bit in your conversion flow (ie to before you deliver results) and it works! Conversion increases throughout the funnel! So you keep it.
Dark patterns like this persist because they measurably work. Some people (you and me) get extra pissed off, but we're in the small minority relative to the people who sign up at an elevated rate. :(