With all due respect because the app is great otherwise, this makes no sense to me as a design choice. You can either
1. Make the ringtones section maybe 2x longer for some users by adding the sounds from /ringtones. Arguably this is a feature and not a bug since you get access to more choices and ringtones sound like alarms anyway and the longer list isn't going to kill anyone. This screen is already full of long lists.
2. Make the app search in /ringtones as well as /alarms, but only if it detects a Samsung phone.
3. Break core functionality for all Samsung users, Samsung being by far the most-purchased brand of Android phones worldwide.
...and you're going with #3? Having so many of your users go through and save each alarm tone individually in whatever third party app they find is not a reasonable solution.
Note for others seeking a workaround: Android alarm/ringtone sounds are kept in these folders:
/system/media/audio/alarms
/system/media/audio/ringtones
/system/media/audio/notifications
Samsung doesn't use the /alarms folder though. Everything is just in /ringtones and the native Samsung tone picker looks in both folders.
I solved the problem by copying everything in /ringtones to /alarms. You could do it more carefully if you don't want duplicate entries in the native picker. I believe you can put these folders anywhere on your device as long as they're called /alarms and /ringtones.
However, if you're not rooted you won't be able to access the system folder.