> Why does the developer console open on the bottom

Actually, the developer console has defaulted to the right side on new profiles for a while now.

For me, vertical space IS at a premium. Especially when browsing the web. How many web pages do you see utilizing the full width of the monitor? Very few, which is also the reason I choose to dock my developer console to the right instead of the bottom. This also doubles as an easy way to resize the viewport when testing responsive design/media queries without resizing the entire window.

Most monitors are 16:9 with the 16 being the horizontal dimension. It's also difficult to read very long lines of text, so my browser windows tend to be narrow and tall. When I use the developer console, I pop it out into another window and put it next to the original window.