If you are to take your phone out of your pocket and happen to toss it on the ground, what will happen you think?. Most obviously it will sustain some kind of damage. Perhaps the screen will crack, the phone may bend a bit or in the worst case it will stop working all together if the electronics get damaged inside the phone.
You might argue that smartphones are not meant for tossing around in the ground. Yes, you are correct in your argument but however smart it may be, it is a mobile device, by definition, it is to be carried along by its user at all times. There are situations when having a smartphone with you is just an inconvenience, where you have to actively look after your phone. Also, there are people who might have to work in an environment which is not so smartphone friendly.
The previous generation of mobile phones were rather durable, but today’s smartphones are not made like that. They are powerful but delicate. If you are bothered by the delicate design of smartphones and looking to buy a new one, then please follow the link to 7 Most Rugged Cell Phones of 2015 to learn about the choices you have available to you. The phones on the list are not only powerful but also meant to survive rough conditions.