The main reason you can’t move apps to an SD card is just because you can’t. As good as Android Operating System is, it doesn’t have a built-in feature that allows users to transfer existing apps to the SD card. You need to rely on third-party apps to enable your phone to move apps. You can try using an app called Lucky Patcher, which will allow a properly mounted SD card to receive installed apps from the phone. However, you need your device to be “rooted” in order to use Lucky Patcher itself. To “root” a phone is essential to open up the Android OS for easy altering or upgrading.
To do so, install Kingo on your PC, plug in your device to the PC through USB, connect it to your phone (make sure your phone debugging mode to launch when connected to USB, under Setting-> General->Developer options), open up Kingo, click to root. The device will then prompt you to install MtkCamera, agree to its condition, let your phone reboot and your phone should now be “rooted”.
Or you can just install Towelroot through their homepage. Ensure that your phone allow apps from “Unknown sources” to be installed (Setting-> General-> Security-> Device administration). Install it and boot up the apps. Follow the instruction one the app, your phone would then reboot and be “rooted”.
Do install an anti-virus app such as SuperSU to protect your phone, since “rooting” the phone opens it to malicious apps.
Once that is done, you should be able to move the apps you want to the SD card back and forth with the Lucky Patcher. Better than buying a new phone to get more memory. Enjoy your now unlocked phone capability. Use it with great care.