Why there are no seo optimizers with a guarantee?

Question

Search Engine Optimization

The first is why there is not a single performer who would say "if in six months these 100500 requests are not in the top, then I've been talking all this time .... or doing something wrong, so I'm returning the money. (I mean in a period of time when Yandex or Google did not change their ranking algorithms there).
Secondly, there is generally someone who does both search engine optimization and work to increase conversion. That is, let's say they brought to the top, a crowd of visitors, and 0 leads, 0001%.

Answer 1

1) if in a simple way - because there are many factors in SEO that cannot be influenced directly and 100%. can only point in the right direction. but whether it will go in this direction or not, and if it goes, then when - no one knows.
2) yes. It's called "Lead Generation"

Answer 2

Exactly because there are no programming courses with guaranteed employment.

Answer 3

because AdWords and Direct with their auctions constantly change the price, and the customer doesn’t have enough money for 100,500 requests, everyone strives to hit SEO