If your garage door is metal or vinyl it is much more difficult and even impossible to fix.
Garage door exterior surface cracked.
Caulk paint cracking or crawling the cracking of the paint film over a caulked area.
The bottom portion of your garage door is most susceptable to this kind of wear which can lead to water damage and wood rot.
Repairing the doors requires a little work and depending on how large the crack is could be.
Gravel and or sand on top of the sub grade.
You are more apt to see these types of cracks on a garage floor that has a hard smooth troweled surface than one that has a broom finish.
Loss of caulk s initial adhesion and flexibility causing painted caulk to crack and or pull away.
Wooden door patch repair an old wooden garage door made of fiber board wood or other composite wood materials can become warp and receive water damage from years of rain and snow splashing and pelting its surface.
If the garage door panels are wood then yes a garage door panel that is cracked could be fixed using wood fillers and glue.