Firstly, they want to make sure that their website looks exactly as they wish. They often end up forking out quite a bit of money to achieve this goal. It can often take a lot of time, too. Some of the more in demand web designers have busy schedules, after all.
Then they let it sit for a while. Quite a few of them seem to get package deals in which the site is designed, built and "optimized for search engines" by the same company.
They believe they've done pretty much all they need to do. They assume that if it's in Google, potential customers will be finding it via various searches.
But as the weeks and months pass they get very few calls from people finding them exclusively online, or none at all. So they then they start to wonder just how many people are arriving via search engines. If they haven't got visit tracking tools already, they get them installed so they can find out these numbers. They are almost invariably disappointed when they discover what they are.
It's at this point that they resolve to do something about getting found online. Many of them employ an SEO company. Sometimes they make a good choice, but because they have so little knowledge they often get ripped off by some slick promotional material that promises the world and delivers very little. If the latter situation eventuates, after several months they stop forking out for the service in frustration and commence looking into doing it themselves. This point often comes at least a year after they had the website made.
My advice: Invert this whole process. Don't worry so much about the aesthetic aspects of your site. While it's desirable to have a visually appealing site, in the end this will have little to do with how Google and the other search engines rank it for various keywords and phrases.
You should start learning about SEO as soon as you can, and get into the habit of applying this knowledge yourself.
Perhaps the most powerful thing you can do -- and it's very simple, requiring next to no technical nous -- is to get your domain in front of as many influential bloggers and webmasters in your niche as possible. Two of the best ways to do this are by writing quality comments on related blogs, and getting active on social media.
The wheels of Google move slowly. So the sooner you can sending it good meaningful signals about the quality and content of your site the better.