When there are multiple affiliates involved in one transaction, payment gets much more complicated. Sometimes it’s even possible for affiliates to jump in at the last minute and claim commissions for customers brought in by other affiliates. Successful programs use multi-channel attribution to ensure the affiliates that create the most value get paid the most.
If you have pop-ups and optins on every page, I would have to think that it would be a lot harder to convince someone to link to it. Especially since the pages where you have your optins (and probably receive the most traffic) are probably the same pages that you have your best content on as well that you'd be hoping to pitch in your outreach campaign.