Clients come in as many forms as users.
Some clients don't realize that they should be asking for something that is legible to their viewers. Of course it may be egotistical of the client to think this way, they may well indeed know their demographic that well, they may not. There are plenty of designers out there to capitalize on those types of clients and not taking the time to point out that there's more at stake than the person who is paying for the site. These designers make work for the other designers who do know how to design for the user and will take the time to try and educate the client. Unfortunately, one has to assume that most users just plugged into the digital revolution today and don't understand a thing about it.