Fixed desktop navigation at the bottom

Navigation at the bottom on mobile is quite popular. However, it hasn't been adopted on desktops much. Is there a reason other than users know to look at the top?

Obviously, for a government or big corporation website, it makes sense to have the navigation in the usual place. What about a 5-page developer portfolio? Does it interfere with accessibility or usability? If the page was scrollable would it be best to hide the navigation?