As with all things email, they probably really wanted to make sure that the mails were delivered and thus were using a commercial MTA to ensure that.
I'd wager, even at 20 or 30 or 40k a year, that's way less than it'd cost to host infra and have at least two if not three engineers available 24/7 to maintain critical infra.
Looking at my mail, over the years I've gotten a couple hundred email from them around certificates and expirations (and other things), and if you assume there's a couple million sites using these certs, I could easily see how you'd end up in a situation where this could scale in cost very very slowly, until it's suddenly a major drain.
Okay I have to ask: if you don't know someone's gender, but you can't call them uh, they/them, then what in the fuck are you supposed to do exactly?
Like, I fully get doing it in person can be being a dick, but on the internet where you absolutely do not know unless someone tells you?
That's the dumbest thing I've heard today, and I was on reddit earlier.