Why does it take months to rank higher on SEO?

Because search engines don’t crawl the entire internet every few days, but every few months

Because the temporal factor is the hardest one to game. Thus a strong predictor of quality/spaminness. Spammers used to do churn and burn and rank in a month or so. This has been killed mid 2013.

From my experience (SEO consultant for 6 years), ranking high can happen almost immediately. It just depends what website you're trying to rank. Google's algorithm values authority heavily. And one of the things that isn't very authoritative is if you have a brand new domain. So if you want to get around the whole "SEO takes time" thing, you have to acquire a domain that has been around for a long time in the space/industry you're looking to rank content in. If wikipedia posted a article tomorrow on a topic, chances are they will rank high the next day for that topic. But if a brand new domain published the same content, it would take much longer and more effort to achieve the same result due to the disparity in authority. Also there's only so much room on page 1 of Google. Not everything is going to rank high that is the nature of SEO.

Generally, SEO is an opaque algorithm designed to prioritize content that is most likely to add meaning to users (therefore increasing their own importance) or advance an agenda (therefore benefiting the organization).

Unfortunately, the internet has devolved in the past few decades from a repository of variously-inclined content builders into a comparatively fewer set of monolithic semi-walled gardens.

To that end, SEO requires an ever-increasingly complex set of trivia regarding a few aspects:

1. The social media networks most likely to favor outbound links to your domain (pro tip: they all favor inbound links to their domain, then typically domains of other monolithic semi-walled gardens). 2. The means to gain traction in each of those semi-walled gardens, which varies heavily by domain, but effective distills to stuffing the magical set of keywords and hashtags at the correct timing. 3. The precise set of keywords on the site itself. They must strike a delicate balance between creating an easy x-ref to their social media presence, but also human-readable enough that people will navigate through a few pages (and therefore not adversely hurt the bounce rate).

I'm absolutely sure I'm missing a few details, but that's the general gist of the SEO business from my own deep dives.