Replication came later - but the fact that you could do

  sudo apt-get install mysql-server mysql-client
  sudo -i mysql

and be logged in as admin into mysql database was indeed a huge reason for defaulting to it.

EDIT: Of course, at that time, there was no Ubuntu teaching everyone to sudo all the time, so drop all instances of sudo and add a su - at start ;)

MySQL has had replication since May 2000.

Replication being easier as driver for developers defaulting to MySQL

Mysql also came with pretty much any webhost.

That's exactly my point. A lot of people started with dynamic websites by using cheap webhosting that you FTP'ed your PHP files to, and used PhpMyAdmin to manage your smallish database, and 2000-2009 they still formed a strong portion of market for starting out (I chose 2009 because that's when EC2 becomes more accessible for this due to RDS)

> Of course, at that time, there was no Ubuntu teaching everyone to sudo all the time

Maybe that's why I am used to logging in as root rather than a user. I started in 1999 and have been surprised how few users now do

Most prod configs I've seen now days disable SSH-ing in as root and password auth so it just becomes:

$ ssh user@server <rsa key> $ sudo -i <user pass> #

Yes, replication. MySQL made it dead easy to have DB clusters in minutes.

I'd wish PostgreSQL would have as simple when it comes to replication and failover like MySQL does. It's always a pain when switching masters back and forth.