Recently new vulnerabilities like Zombie POODLE, GOLDENDOODLE, 0-Length OpenSSL and Sleeping POODLE were published for websites that use CBC (Cipher Block Chaining) block cipher modes. These vulnerabilities are applicable only if the server uses TLS 1.2 or TLS 1.1 or TLS 1.0 with CBC cipher modes.

Another reason to push TLS 1.3 as much and as quickly as possible. is already marking all CBC cipher suites, as well as versions of TLS lower than 1.2, as "weak".