Why did you have to "go back" to get to Gen 5? When you click to Gen 4 there are the same links to other generations there, too. If you need to compare both generations side-by-side you can open the two pages in separate tabs or windows.
The generations are kept separate because that is the easiest way to read them. Having everything in one huge table is really messy, and would make the Pokedex page even slower to load.