I don't think it's just us getting old. Newcomers to the filed don't really understand HTML and CSS. It's just "React components" to them, and they aren't looking deeper than that.
There are a lot of reasons to have abstractions over HTML/CSS in emails, for all but the trivial cases. It is notoriously difficult to get right, since there are some features lacking and standards in the email client space moves way slower than browser.
A regular marketing HTML email would look unrecognizable to a lot of old timers.
For a major brand, CSS and pretty design is a requirement for all branded emails.
For that having a React wrapper that makes the hard parts easy makes total sense.