StartSSL and WoSign have been offering free, publicly trusted certificates with one year lifetimes (and the ability to renew for free) for quite some time.
The former doesn't allow commercial usage, while the latter operates in China. That's probably why it wasn't an option for a lot of people. (That, and the terrible UX at least in StartSSL's case.)
StartSSL isn't free. They charge for certificate revocation.
Furthermore, their free certificates cannot be used for commercial purposes.
I don't know why your comment is downvoted -- this is acutally a legitimate issue mentioned in their terms of service.
StartSSL generally don't mention their terms, so a lot of the use of 'StartSSL Free' is commercial. People don't like to hear they've been misled (and shoot the messenger).
They actually started policing this and refuse to renew a certificate if they decide it's a commercial use. Happened to me and rather than argue with them (it wasn't), I bought a $5 one at ssls.com...
While I agree LetsEncrypt is awesome, the certificates are actually shorter-lived (90 days), I believe, than the former CAs that issued certs for free (e.g. StartSSL) that offered a year of validity. The rationale is replacing the keys sooner since you can easily do it automatically with LE.
LE made SSL free, trusted and long-term. You could have made it twice as hard to do the initial setup and people would have jumped at the opportunity regardless.