Why hbogo app does not work for macbook air? Why so few apps in Appstore for Macbook Air?

I have been able to download HBOGo app and HBO Now but they only sit in my iTunes download section. I cannot get either to open. Also, why are there so few apps for Macbook Air compared to what is available for iPod and IPad? Science apps are piddling, few entertainment apps. I don't play the games and am not a developer. I wish I had known before purchasing, Will there be new Apps debuting regularly?