Glass has several advantages over graphite. It's better at fighting fish, and it's much harder to break. It's (sometimes) easier to make a delicate presentation with. And it's cheaper than split cane.
Add that to the fact that many of us prefer casting glass to graphite, it's not surprising that it's made a comeback.
For situations where a a rod of eight feet or shorter is appropriate, it's hard to beat glass.
Modern glass isn't even all that slow. My Orvis Superfine Glass is faster than many of my graphite rod.
I wouldn't want to use it in a Euro nymphing rod, but I fish both vintage and modern glass quite a bit.