...Along with replication and being joined with the hip to PHP. As to installation, there was a point in time in the early 2000s where you could sudo to root, type 'mysql' and be talking to a live MySQL on most Linux distros that I used. No wonder a lot of people defaulted to it.
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 ;)
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
$ ssh user@server <rsa key> $ sudo -i <user pass> #
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.