Why did Hitler want the area called the Sudetenland?
Because it had a large German population.
As I said the Sudetenland had a large German population and therefore Hitler saw it only natural that this area should be part of the German Reich. It should also be noted that he said his annexation of the Sudetenland would be his last territorial expansion, a promise he would of course later go back on.
This was also related to Hitler's idea of "Lebensraum" and how the German population was entitled more "Living space for their population"- something he would outline in "Mein Kampf".
This can also be seen as yet another act of defiance made by Hiter to go against the Versailles peace treaty of 1919- as he despised the treaty and called it a "diktat"(something which was forced upon the German people), and hence he wanted to try making Germany stronger. This was because The Versailles treaty had weakened Germany both militarily and economically due to the restriction on military and forced war-reparations.