If you’re using an Android phone, you might want to read this thread: https://forum.inaturalist.org/t/android-app-not-reading-picture-location-data/37908/26 . Newer versions of the Android photo picker are not transferring image location data to the Android iNat app. There’s a workaround that switches to the old photo picker: https://forum.inaturalist.org/t/android-app-not-reading-picture-location-data/37908/9
Of course, that may not be your issue at all. And if your phone truly didn’t record the location on many photos I feel for you.