I put ground beef in the fridge 3 days ago and it's still frozen! Why isn't it thawing like normal?
Either you've insulated it or your fridge is really cold. I suggest using a thermometer to check your fridge temperature.
Parts of your fridge may be at slightly different temperatures than other parts; it may help to move it to a warmer part of the fridge (if that can be done safely, you don't want it dripping on your produce, for example).
You could use the cold water method to defrost your ground beef if you're going to cook it all once its defrosted. The USDA has thawing instructions. Generally, I'd avoid microwave-thawing ground beef, unless its going into chili or similar, because those cooked bits on the outside prevent forming it into patties, etc.
Other possibile reasons are. 1- the meat has a different water content than usual (you buy the same packet but they change suppliers), or/and 2- pick and save just got it from the storage freezer (-30C to the shop floor freezers (-18C) when you got it home it was still super frozen and it's going to take longer to thaw.