A lot of SEO work is correcting mistakes made by web designers
Web designers commonly create websites that don’t have friendly URLs. They create sites that contain no keywords and use “Welcome to COMPANY NAME” as the title tag and H1 on the homepage.
They create sites that have dull content that focuses on how wonderful the website owner is - because they abdicate responsibility for creating content to clients with no advice on how to do it well.
SEO consultants then get paid to offer useful advice like “had you though of having something interesting on your site?” and “had you thought of having friendly URLs” and “perhaps we should add a blog”.