The system has been in place for at least 50 years. In my mum's day it was a common past time for her and her brothers to go hunting for what they called "glass cheques". The idea is to avoid it ending up where it shouldn't by incentivising good behaviour. If people can return the glass for money then few of them end up on the beach.
It's much better in almost every way besides weight. Much more reusable, not leaking any chemicals in soil/water/our bodies, &c.
Glass is inert and doesn't break down; anyone can pick up glass bottles that have been on the beach for decades, wash them out, and recycle them along with new glass.
Metal degrades slowly if it's ferrous (iron/steel), but that isn't environmentally harmful. And it can all be readily recycled.
I think the implication was what if some jackass smashes the bottles and you find them with your foot.
I feel like that is a pretty insignificant issue compared with 8-20 million tons of plastics ending up in the sea.