Maybe a weird design decision but it never bothers me. I don't use search a lot, but when I do I just press End on a desktop browser to immediately scroll to it, or on mobile I fling the page all the way down to the bottom. Doesn't bother me, personally.
I also kind of appreciate the fact it doesn't take up space above, so the search field is a little bit wider than what is normally available in other sites where it is on top.