ProSeries is a very complex application, on the order of millions of lines of code.. which leverages probably billions of lines of code written by other teams and companies. If you look at Microsoft alone, over the years they've introduced (and deprecated) about 5 radically different ways to create desktop applications. Every year we are constantly updating things to newer technologies, to ensure we don't one day find ourselves with something that's impossible to work on and to minimize risk of something breaking all of sudden with some new Microsoft update.