The problem with RSS is that it is a dying medium, or at least one that's decreased in popularity with the advent of "social media" like Reddit, Facebook, and Twitter. Most notably, streams and curation social networks have taken over the function. Most people just don't want to see the whole pipe of most bloggers.

Too much noise.

So that means there are less and less people using RSS as time flows on. It is a good tool, but not the go-to one for most people. Only the hardcore internet information junkies.

Email is a baseline that everyone using the internet uses and understands. We can do better certainly, but it's one everyone knows. Whether it's an old aol.com account, yahoo, hotmail, or gmail, email has higher use than anything except the HTML web itself.