In general, autoclaving glass is not difficult, and we do it every day with macro-sized lab material (flask with a volume of 100 ml+, large pipettes (10 ml+) etc.)
But given the ongoing miniturization in science, we use plastics for everything that requires volumes in the range of 1 µl - 10 ml. And we use A LOT of that stuff. At that scale, glassware is very hard to get clean and sterile once it is used. And ofc, glass only has an environmental advantage IF it can be reused.
That's what I meant with my sentence, thanks for pointing out the missing explaination.