Hey,
I made the alarm app called Interval which you might like. Its just had an update as well. But I can explain to you why no app seems to have the big snooze buttons.
When the app schedules an alarm with the Windows Phone system, what you're really doing is asking the operating system to schedule one for you. It has its own way of displaying the alarm when it goes off and your app cannot edit that. So in short, when your alarm goes off, its not the app doing it... its the Windows Phone system.
Annoyingly, you can't just do it yourself and create your own scheduler within your app because Windows Phone doesn't currently let you run stuff in the background in the same way you can on android. There's an option to run things every half hour or so, but not in "real time" so to speak. So at the moment you won't find an app that has custom alarm screens :-(