Enable Landscape rotation quick settings toggle on unrootable Moto G (maybe using ADB?)
This app can lock your screen in landscape: Rotation Locker - Google Play and doesn't require root. I recommend this app because it has no permissions, is &lt;100KB (no ads), and if you use Tasker, this app also has Tasker integration.

The explanation for your problem is that carriers and phone brands often decide "you don't need this feature" and just disable it on the front-end. But they don't actually spend the time to really disable that feature. The app works without root because Android provides an API to lock rotation, that's just part of Android.

Hope this helps solve your problem!