1. I can send a letter to anyone, because anyone has an address. Not everyone has an email address. Plus I can add small physical things, and it's more personal with handwriting and a little perfume ;).
2. If I need quick communication, I just call them.
A lot of arguments that are anti-blockchain and anti-cryptocurrency (based on other tech besides blockchain) can be used in the same way with email.
I can give you pretty convincing arguments why email will fail because we already have traditional snail mail (which can do a lot more), and phone (which is faster and more direct).
Fact is that cryptocurrencies, smart contracts and other blockchain applications live 100% on the internet, which means it's faster, cheaper, simpler, global (= not tied to countries and specific companies)