Generally speaking, most sites drag the most important top-level navigation in the upper right corner. Thus, it is natural that the importance of entering the site also falls into this place. Since the logo for the site goes in the upper left corner, the place that is most likely not to behave badly regardless of which browser you are viewing on the site ... the only remaining most noticeable place on the page, of course, is in the upper right the corner!
There are many books on usability, because for some reason this happened. There are also many studies in which people pay attention to the most frequent place on the site, which led to the choice of these places. The actual scientific facts underlying these layouts.
Why amazons where it is ... more research, I think!