Well it is going to depend on what version of Android you are using and what device you are trying to move them on. If the device is Samsung or LG it is completely possible that it has been restricted by them as they are both manufacturers who are restricting this option on their devices.
Also, if the phone is running anything below "Marshmallow" there is no way to move 'all' apps to an SD card. Only "Marshmallow" allows that option.
Now if you have a device that allows it and are running "Marshmallow" as well, then I would ask if you have updated anything recently and if the problem started after an update. If it did, I would see if the update is removable.
Lastly, if (as stated above) have a phone that is running "Marshmallow" and...