The law is understandable. If people come with glass bottles of beer or coke or whatever to the beach, soon enough there will be broken bottles and shards of glass in the sand tearing up people's barefoot feet.

Nobody wants that.

I guess the law's existence is not well known, and I have no idea if signage at the beaches is adequate or not - I do not recall seeing such a sign but maybe I just did not pay attention to it. if there isn't, there should be better signage. I would guess it is probably included in the large sign at the entrance to every beach with the rules that nobody reads.

To be fair, while it makes sense to ban glass bottles at a beach, the beach kiosk should not be allowed to sell glass bottles of beer (or other drink) either.

Hamechadesh is reporting on a situation in which several yeshiva bochurim who went to the separate beach in Tel Aviv who were slapped with these significant fines immediately upon opening the bottles that they had just bought from the beach kiosk.

While ignorance of the law is almost never a good defense for being caught breaking it, the boys complained that they had just bought the bottles from the beach kiosk. 

Now that is not right. 

I am not saying they should not get fined for drinking from a glass bottle, but the kiosk should not be allowed to sell drinks in glass bottles if it is illegal to drink from them on the beach. Nobody is buying beer from the beach kiosk to stock up their fridge for Shabbos or to restock their depleted pantry. They are purchasing in the beach kiosk to drink on the beach, and if it is illegal to drink this on the beach it should not be sold in the beach kiosk.