Since I started out as a web designer back in the mid Nineties, I've long been involved in my local community. Since that's where most designers find their clients, its only natural that these same people want to now help these companies promote their wares locally, and globally.
When I started out, I was doing static websites; just helping businesses get online. And I'd be willing to bet that most web designers are still that way. They don't understand marketing. They don't understand search. They don't understand advertising, and they don't want to. They want to make a set of pages, FTP them up, bill the client and move on.
This puts their client in a bad situation. So the client has this new (unoptimized, most likely) fancy website. Most small businesses put out a good chunk of change to get their sites built, and then they think the people will come. Build it and they will come, they think.
Not on the Internets, they won't.
The 'BIATWC' mantra is a far cry from true on the world wide web. More like 'Build it and no one will notice' if you ask me. Web designers who are purely building websites and dumping them onto the web are doing their clients a huge disservice. Sure, they're doing what they're paid to do, they do good work, and they provide just what the client asked for.
The problem is that most designers really have no idea that they're even doing this disservice. They have no idea what is involved in marketing a website, and (for the most part) they prefer to stay ignorant of those skills. They still tell their clients to supply them with ten keywords for the meta tag so they can rank well. And they're the same ones that are still putting each state name in those tags, too.
So what's the lesson here? Simple. Learn what you're doing. Believe it or not, every web designer is also in marketing. That's what you're ultimately selling your client, right? Another way to market their business? So if you don't know the marketing aspect of it, make sure (at the least) that you hand off your crappy code work to a professional SEO/SEM when you're finished raping them for that fancy design.