First, cost is subjective. Not all SEO work is expensive.
Competitive search queries take time to achieve market shares. Higher volume keywords are typically more difficult.
You may have low domain/page authority. Sites linking to you are votes in the eyes of the search engines. And in case you don’t have link worthy content, that has to be developed and created, keeping your goals in mind. Then, as SEO experts, we must perform outreach. That takes time.
In many cases, websites are poorly designed. They have a confusing navigational structure, have poor internal link structures, or may respond slowly.
It may also be necessary to migrate, if the site is simply too old to function.
With the constant shifts in technology and changes in consumer behavior, it also takes time and research to understand the target audience.
The best SEO practitioners stay up to date, anticipate, and prepare you for change. The best SEO agencies in KSA will do everything it takes to help you understand this. Their chief responsibility is maintaining market share and building on it. Google is constantly changing its algorithm and new competitors are also constantly entering the space.