Here's what Let's Encrypt says in its post:
"Much more work remains to be done before the Internet is free from insecure protocols, but this is substantial and rapid progress. It is clear that the cost and bureaucracy of obtaining certificates was forcing many websites to continue with the insecure HTTP protocol, long after we've known that HTTPS needs to be the default.
We're very proud to be seeing that change, and helping to create a future in which newly provisioned websites are automatically secure and encrypted."
Also Read: Hackers Install Free SSL Certs from Let's Encrypt On Malicious Web Sites.