>> Joomla is a self build system.
Yes. But as a web designer I'm not going to tell my clients to build their own sites with it. Most clients would not even even have the skills to maintain the content let alone set it up.
The point is webdesigners need a solution for their clients as Jekie suggests, e.g. simple and it takes no time to setup and learn.
If the client does not have the budget for you to make a proper site then at least have an instant site builder solution to offer so you can make a bit of money from them.
Either way, Joomla is certainly not the best solution for this type of smaller text based site anyway.