It is historical. See: http://mysqlserverteam.com/mysql-8-0-when-to-use-utf8mb3-over-utf8mb4/ http://mysqlserverteam.com/mysql-8-0-when-to-use-utf8mb3-ove...

It is historical. See: http://mysqlserverteam.com/mysql-8-0-when-to-use-utf8mb3-over-utf8mb4/ http://mysqlserverteam.com/mysql-8-0-when-to-use-utf8mb3-ove... http://mysqlserverteam.com/sushi-beer-an-introduction-of-utf8-support-in-mysql-8-0/ http://mysqlserverteam.com/sushi-beer-an-introduction-of-utf... (Problem #1) (Author is the first link here.)