You are talking of a volume of around 600 000 000 domains (based on a plot on their website) that try to renew at best after 8 weeks. And that's just default profile, there are 160h certs profiles now [0].
You think they will ever send nearly as much as (at least) 75 million newsletter mails weekly? Sendgrid's highest value in their pricing slider is 1,25 mil a week.