I think the main issue with glass is the fact that they’re not biodegradable that’s why they’re likely to end up in a landfill, ergo additional waste. Just like plastic, if you keep piling glass, it won’t disappear for a very long time. It’ll just stay there until you move it to another dump site.
So how eco friendly is glass? I think they are still eco friendly even when they’re non biodegradable because they can be easily recycled compared to plastic. It’s hard to recycle plastic because you can’t easily separate the toxic wastes and the cleaner parts.
For glass though, they can easily be cleaned which makes them easier to recycle.
The problem of them ending in a land fill can be solved by strict compliance with waste separation so that unused glass can be easily sent to factories for recycling.