we dont have an infinite ammount of content for high keys,because they are imposible to complete,the hardcore only really have about 4-5 levels that are doable and challenging,the casuals have 1 until atleast 15 or even more if you have better gear
but yeah,i do agree,i wish there was more to do,guild wars 2 is a good example,but where gw2 fails is where wow excels