Good question.
SEO is a long term marketing strategy.
The work itself is time-consuming. The analysis, planning and execution of key SEO optimisation areas like backlink building or content writing takes a lot of time. Google demands high-quality, and if your website doesn’t deliver you just won’t see good results.
Once the changes are implemented it takes Google and other search engines time to recognise the improvements.
All of this combined makes SEO the long road, but often the one that provides sustainable and long term success. Unlike digital marketing options like Google ads, the business you can gain from organic search is free.