I agree with you. It seems that there are a lot of people with this issue.
The crack is along the weldline of the part. The weldline is formed during the injection molding process for the part. The material that they chose is also not UV resistant. So with exposure to the sun, this material will drastically degrade. With temperature cycling, hot summers and cold winters, and people using the door bell, the button fatigues. Once fatigued, a crack will start in the button. Some more solar radiation and temperature cycling will propogate this crack.
WIth a proper design and testing and good molding this problem could have been avoided by Ring. Ring should have determined that they had this problem by doing a temperature cycling test with solar radiation exposure. Poor design and design processes.