Just curious, are you talking about Webflow? Because I had to hunt down and make sure our Let's Encrypt auto renewal was working until I realized the certificate was served by them. They wait until the last 12 hours to renew the certificate. I have no idea what type of rationalization would lead to that decision.
I had the same thought, but I still find that absurd. Say they host 500,000 websites with HTTPS. 1,000,000 renewals they save spread across the year, roughly 2 renewals a minute. That is pennies. A t2.medium could handle that type of load increase