SEO takes so long because there are several factors involved to get results: SEO keyword difficulty, competition, inbound links, and domain age. Therefore, SEO can take a longer or shorter time depending on how you approach these key search engine optimization areas.
It takes time to earn a PhD, gain a following, or earn the trust of your peers and audience. Google understands this, and they also know that it takes time for these accomplishments to be reflected online. That's just one reason why the SEO process is so slow.