Returned bottles have a finite lifetime after what they have to be trashed. Glass bottles tend to be reused some (small) tens of times, plastic bottles certainly last a lot less.

Google AI is saying 25->30 on average with a high of 50.

That still ends up being translated to 1/2 to 1/3 (up to 1/5th) the energy of plastic.

Glass is also one of the few good cases for recycling.