Unfortunately, the popup Google chose to use looks like an advertisement. The red "new" banner and animated gif.
They might have reacted differently to an actual dialog at first click that says "This will inject an image into your outbound email, and mute the conversation. Continue?" (with the default choice set to "NO".
They might have reacted differently to an actual dialog at first click that says "This will inject an image into your outbound email, and mute the conversation. Continue?" (with the default choice set to "NO".