SEO is important to fashion as it drives long term traffic growth thanks to the positioning of your website in the top results of the Seaerch Engine Results Page (SERP). This is by definition free traffic that you don't need to pay for and it is generally 'long lasting', once you are in the topo position of a search engine for a specific keyword you are likely to remain there for some time. While when you invest in Ads you need to keep paying to appear in the SERP.