Mailchimp is "big tech" now? Can't these folks just throw a RSS feed together (hosted on the cheapest static webhost around) and tell people to subscribe to it? This is a big fat nothingburger if I ever saw one.
Because to a first approximation everyone understands, and can get, email, while maybe 5% of the population, if that, understand RSS feeds. My 80 year old aunt can read email. While I'm sure I could teach her to use RSS feeds, it would not be a task I would look foward to. And she has me. Most people don't have me, or anyone like me (or, likely, you, or the majority of other users of this site). What you're saying is…
At some point in history, 5% or less of the population understood email. RSS feeds are not inherently more complex than email, in fact they're quite a bit simpler. (And even if you don't grok RSS feeds, you'll probably grok a weblog; RSS is only relevant here because it gives the exact same affordances as something like a Mailchimp newsletter, even though it works differently under the hood.)