Marty has a Samsung Galaxy S5 with 16GB of RAM and a 64GB memory card. When the apps update, however, they install back onto the internal storage. Leo says that SD card storage is an issue on Android. They can't put apps on an SD card if it uses widgets. So some apps will move back. It's probably why Apple doesn't mess with it.
The chatroom says that the S5 update to Android 6.0 solves that problem, if he can update. It's called Adoptable Storage, but it was really only a Google feature. The SD card is really meant for media and storage, not for apps. He should get a new phone.