Broken glass everywhere

Today one of my friends and I met up for coffee in the morning hen took the dogs for a walk and was a lovely walk until all he glass. 

This is glass my friend picked up in an area where people and dogs walk all he time and it's close to high school. Second picture heavily edited to show the amount of glass on another path where people and dogs walk. And they are all bottles of beer. 

There is so much glass everywhere here and it's a deliberate act for people's dogs to get injured. No idea why they would do such a thing also is all over a forest walk too. I really do not understand people and why this is a thing they would do. Angry doesn't even cut it