There are a few reasons.
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First, web design is a specialized skill. It takes years of experience and practice to become an expert web designer.
Second, designing and building a website is a time-consuming process. It's not something that can be done in a few hours or days.
Third, professional web designers have the latest tools and technologies at their disposal, which means they can build websites that look good and function well.
Finally, professional web designers know how to design websites that are search engine friendly and that will rank high in search results.
So if you're looking to launch a website, it's definitely worth hiring a professional web designer to do the job for you.