Sure, it's great in that one metric. But annoying me with the offer to get a bunch of emails I don't want isn't making me like your site.

Even if I was the odd one and nobody else would mind those pop-ups: In the context of multiple experiments showing that a few hundred milliseconds additional page load time have a very real impact on engagement rates it stands to reason that interrupting the user experience with unrelated email sign ups should have a similar effect.