Only about 30% of "recycled" glass is actually recycled in the USA and its going down with a lot of municipalities removing it from their programs completely.

In short because glass breaks and contaminates paper and aluminum plus needs to be sorted by color it costs too much to handle and economics are more important than environmental externalities.

There are concerns about the weight of glass (energy cost), the energy required to create and recycle, the likelihood that even things like "reusing beer bottles by just washing" have risks with glass chipping or having cracks that extra costs to reuse. I'm less up to speed on all of these costs and risks so take with a grain of salt.